Description of problem:
According to the comments of virInterfaceDestroy, the destroyed interface should be brought up after rollback:

        If there is an open network config transaction at the time this
        interface is destroyed (that is, if virInterfaceChangeBegin() had
        been called), and if the interface is later undefined and then
        virInterfaceChangeRollback() is called, the restoral of the
        interface definition will also bring the interface back up. """
  
But it's not in my test. Actually, I found netcf just restore configuration on rollback and didn't handle the activation of interface. So perhaps we need fix that in netcf at first.

Version-Release number of selected component (if applicable):
libvirt-0.9.11.4-3.fc17

How reproducible:
always

Steps to Reproduce:
1. create interface:
virsh # iface-define /home/mark/Work/xml/em1.xml 
Interface em1 defined from /home/mark/Work/xml/em1.xml
virsh # iface-start em1
Interface em1 started
virsh # iface-dumpxml em1
<interface type='ethernet' name='em1'>
  <protocol family='ipv4'>
    <ip address='9.115.122.89' prefix='24'/>
  </protocol>
  <protocol family='ipv6'>
    <ip address='fe80::221:ccff:fe68:d738' prefix='64'/>
  </protocol>
</interface>

2. begin a transaction and destroy interface:
virsh # iface-begin 
Network config change transaction started

virsh # iface-destroy em1
Interface em1 destroyed

3. rollback
virsh # iface-rollback 
Network config change transaction rolled back

virsh # iface-dumpxml em1
<interface type='ethernet' name='em1'>
</interface>

Actual results:
em1 is not in the out of ifconfig, because it's still down after rollback


Expected results:
bring up the destroyed interface after rollback

Additional info: