Bug 1309232

Description of problem:
As we already fixed some useful options for attach-interface command. the same issue still happens on detach-interface command. perhaps it also needs a fix.

Version-Release number of selected component (if applicable):
libvirt-0.10.2-57.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1.check with virsh help:
# virsh help detach-interface
  NAME
    detach-interface - detach network interface

  SYNOPSIS
    detach-interface <domain> <type> [--mac <string>] [--config]

  DESCRIPTION
    Detach network interface.

  OPTIONS
    [--domain] <string>  domain name, id or uuid
    [--type] <string>  network interface type
    --mac <string>   MAC address
    --config         affect next boot


2.check document 
detach-interface domain type [--mac mac] [--config]
Detach a network interface from a domain.  type can be either network to indicate a physical network device or bridge to indicate a bridge to a device. It is recommended to use the mac option to
distinguish between the interfaces if more than one are present on the domain.  If --config is specified, alter persistent configuration, effect observed on next boot, for compatibility purposes,
--persistent is alias of --config.

3.use --config to detach, it works as --persistent, no only for next boot, but also works for current running states.

# virsh dumpxml r6 | grep interface -A 4
    <interface type='network'>
      <mac address='52:54:00:aa:b4:a1'/>
      <source network='default'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
--
    </interface>
    <serial type='pty'>

# virsh detach-interface r6 --type network --mac "52:54:00:aa:b4:a1" --config
Interface detached successfully

# virsh dumpxml r6 | grep interface -A 4
# virsh dumpxml r6 --inactive | grep interface -A 4
Nothing output.

Actual results:
As above.

Expected results:
Fix it as same as attach-interface.  

Additional info:
This is only happened on rhel6. Rhel7 already provide other options for detach-interface.