Description of problem:
I booted up a guest with virtio nic, change the MTU of guest nic and tap device
to 65520(max MTU of virtio nic), and added an arp entry on host, then ping
guest from host, but guest abnormally quit. Qemu outputted : "virtio-net truncating packet"

# ping $guest_ip -I virtio_0_6001 -s 65492 -M do
PING 10.66.84.205 (10.66.84.205) from 10.66.85.217 virtio_0_6001: 65492(65520) bytes of data.
ping: sendmsg: No such device
ping: sendmsg: No such device
ping: sendmsg: No such device
ping: sendmsg: No such device
ping: sendmsg: No such device
ping: sendmsg: No such device


Version-Release number of selected component (if applicable):
host kernel: 2.6.18-203.el5
guest kernel: 2.6.9-89.28.ELsmp
# rpm -qa |grep kvm
etherboot-zroms-kvm-5.4.4-13.el5
kvm-qemu-img-83-183.el5
kmod-kvm-83-183.el5
kvm-83-183.el5
kvm-tools-83-183.el5
kvm-debuginfo-83-183.el5

How reproducible:
100%

Steps to Reproduce:
1. Boot up a rhel4 guest with virtio nic
2. Change MTU of guest nic and $tap
guest)# ifconfig eth0 mtu 65520
host)# ifconfig $tap mut 65520
3. Add a arp entry on host
# arp -s $guest_ip $guest_mac -i $tap
4. Ping guest from host  (65520-28=65492, 65520 is max mtu of virtio nic)
#ping $guest_ip -I $tap -s 65492 -M do

 
Actual results:
host can ping guest successfully

Expected results:
guest abnormally quit

Additional info:
1. Command line:
# qemu-kvm -name 'vm1' -monitor tcp:0:6001,server,nowait -drive file=/root/autotest/client/tests/kvm/images/RHEL-4.8-64-virtio.qcow2,if=virtio,cache=none,boot=on -net nic,vlan=0,model=virtio,macaddr=02:70:04:52:e8:e2 -net tap,vlan=0,ifname=virtio_0_6001,script=/root/autotest/client/tests/kvm/scripts/qemu-ifup-switch,downscript=no -m 4096 -smp 2 -soundhw ac97 -vnc :0 -spice port=8000,disable-ticketing -serial unix:/tmp/serial-20100621-161808-MXgd,server,nowait -no-hpet