description of problem:
libvirt should check stp delay time.When you set a large number or a negative number to it,it will start success and can use dumpxml see it.

Version-Release number of selected component (if applicable):
libvirt-1.1.1-29.el7_0.1.x86_64


How reproducible:
100%

Steps to Reproduce:
1.prepare xml like this
# cat net.xml
<network>
  <name>net4</name>
  <uuid>d918f9ff-f9b2-4ab7-ae01-f1042cd303a6</uuid>
  <forward mode='nat'/>
  <bridge name='virbr13' stp='on' delay='-10000000000' />
  <mac address='52:54:00:c7:ce7'/>
  <ip address='192.168.13.13' netmask='255.255.255.0'>
  </ip>
</network>

2.define it and start
# virsh net-define net.xml
Network net4 defined from net.xml

3.# virsh net-dumpxml net4
<network>
  <name>net4</name>
  <uuid>d918f9ff-f9b2-4ab7-ae01-f1042cd303a6</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr13' stp='on' delay='-10000000000' />
  <mac address='52:54:00:c7:ce7'/>
  <ip address='192.168.13.13' netmask='255.255.255.0'>
  </ip>
</network>

4.# brctl showstp virbr13
virbr13
 bridge id                8000.525400c7ced7
 designated root        8000.525400c7ced7
 root port                   0                        path cost                   0
 max age                  20.00                        bridge max age                  20.00
 hello time                   2.00                        bridge hello time           2.00
 *forward delay                  30.00*                        bridge forward delay          30.00
 ageing time                 300.00
 hello timer                   0.93                        tcn timer                   0.00
 topology change timer           0.00                        gc timer                 236.12
 flags                        




Actual results:
Edit success with no error output, network can start normal.And dumpxml cannot
offer a right forward delay time.

Expected results:
libvirt should check stp delay time,and don't