Description of problem:
The value of iothrottling burst_length can be negatives or larger than 1000000000, but checked with a wrong value in qmp

Version-Release number of selected component (if applicable):
kernel: 3.10.0-406.el7.x86_64
qemu-kvm-rhev: qemu-kvm-rhev-2.6.0-4.el7.x86_64

How reproducible:
100%


Steps to Reproduce:
1. Start a guest with iothrottling parameter burst_length on a data disk, and set such as throttling.bps-total-max-length:

/usr/libexec/qemu-kvm -name rhel7.3 -enable-kvm -m 4G -smp 4 -uuid ae361e8d-288b-4e70-8783-bda0d450ce38 -nodefconfig --nodefaults -boot order=cd,menu=on -device virtio-scsi-pci,id=virtio_scsi_pci0,bus=pci.0,addr=03 -drive id=drive_image1,if=none,cache=none,snapshot=off,aio=native,format=qcow2,file=/home/rhel7.3 -device scsi-hd,id=image1,drive=drive_image1,bootindex=0 -drive file=/home/kvm_autotest_root/iso/linux/RHEL-7.2-20151030.0-Server-x86_64-dvd1.iso,media=cdrom,id=cdrom,if=none -device ide-drive,drive=cdrom,bootindex=1 -vnc 0.0.0.0:14 -monitor stdio -netdev tap,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown,id=hostnet0 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=00:52:5a:30:2e:61,bus=pci.0,addr=0x7 -drive id=drive_image2,if=none,cache=none,snapshot=off,aio=native,format=qcow2,file=/home/disk1,bps=102400,bps_max=512000,throttling.bps-total-max-length=10 -device scsi-hd,id=image2,drive=drive_image2 -chardev socket,id=qmpmonitor1,path=/tmp/monitor1,server,nowait -mon chardev=qmpmonitor1,mode=control -vga cirrus


2. Set the burst_length to be a negative value in qmp and check it with qmp cmd '{ "execute": "query-block"}':

nc -U /tmp/monitor1
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 6, "major": 2}, "package": " (qemu-kvm-rhev-2.6.0-4.el7)"}, "capabilities": []}}
{"execute":"qmp_capabilities"}
{"return": {}}
{ "execute": "block_set_io_throttle", "arguments": { "device": "drive_image2","bps": 102400,"bps_rd": 0,"bps_wr": 0,"iops": 0,"iops_rd": 0,"iops_wr": 0,"bps_max":102400,"bps_max_length":-10}}
{ "execute": "query-block"}
{"return": [{"io-status": "ok", "device": "drive_image1", "locked": false, "removable": false, "inserted": {"iops_rd": 0, "detect_zeroes": "off", "image": {"virtual-size": 21474836480, "filename": "/home/rhel7.3", "cluster-size": 65536, "format": "qcow2", "actual-size": 1461977088, "format-specific": {"type": "qcow2", "data": {"compat": "1.1", "lazy-refcounts": false, "refcount-bits": 16, "corrupt": false}}, "dirty-flag": false}, "iops_wr": 0, "ro": false, "node-name": "#block106", "backing_file_depth": 0, "drv": "qcow2", "iops": 0, "bps_wr": 0, "write_threshold": 0, "encrypted": false, "bps": 0, "bps_rd": 0, "cache": {"no-flush": false, "direct": true, "writeback": true}, "file": "/home/rhel7.3", "encryption_key_missing": false}, "type": "unknown"}, {"io-status": "ok", "device": "cdrom", "locked": true, "removable": true, "inserted": {"iops_rd": 0, "detect_zeroes": "off", "image": {"virtual-size": 4043309056, "filename": "/home/kvm_autotest_root/iso/linux/RHEL-7.2-20151030.0-Server-x86_64-dvd1.iso", "format": "raw", "actual-size": 4051255296, "dirty-flag": false}, "iops_wr": 0, "ro": true, "node-name": "#block343", "backing_file_depth": 0, "drv": "raw", "iops": 0, "bps_wr": 0, "write_threshold": 0, "encrypted": false, "bps": 0, "bps_rd": 0, "cache": {"no-flush": false, "direct": false, "writeback": true}, "file": "/home/kvm_autotest_root/iso/linux/RHEL-7.2-20151030.0-Server-x86_64-dvd1.iso", "encryption_key_missing": false}, "tray_open": false, "type": "unknown"}, {"io-status": "ok", "device": "drive_image2", "locked": false, "removable": false, "inserted": {"iops_rd": 0, "detect_zeroes": "off", "bps_max_length": 4294967286, "image": {"virtual-size": 1073741824, "filename": "/home/disk1", "cluster-size": 65536, "format": "qcow2", "actual-size": 118824960, "format-specific": {"type": "qcow2", "data": {"compat": "1.1", "lazy-refcounts": false, "refcount-bits": 16, "corrupt": false}}, "dirty-flag": false}, "iops_wr": 0, "group": "", "ro": false, "node-name": "#block570", "backing_file_depth": 0, "drv": "qcow2", "bps_max": 102400, "iops": 0, "bps_wr": 0, "write_threshold": 0, "encrypted": false, "bps": 102400, "bps_rd": 0, "cache": {"no-flush": false, "direct": true, "writeback": true}, "file": "/home/disk1", "encryption_key_missing": false}, "type": "unknown"}]}

3. Similar to step2, set the burst_length to be 1000000000 in qmp and check it with qmp cmd '{ "execute": "query-block"}'
4. Set the burst_length to be 10000000000 in qmp and check it with qmp cmd '{ "execute": "query-block"}'


Actual results:
In steps 2 and 4, the negative value and 10000000000(10 zeros) can be set, and checked from qmp the value became to 4294967286 and 1410065408
In step 3, 1000000000(9 zeros) can be set and checked correctly

Expected results:
In step2, the negative value is not allowed to set.
In step4, if 10000000000(10 zeros) could be set, it should be checked and worked correctly; and an upper limit should be specified.

Additional info: