Description of problem:
xml created by 'virsh dumpxml <domain>' does not validate with 'virt-xml-validate',when the domain's interface type is 'network'.
And when the domain's interface type is 'bridge',dumpxml can validate with 'virt-xml-validate'.

Version-Release number of selected component (if applicable):
  kernel-3.10.0-309.x86_64.rpm
  qemu-kvm-rhev-2.3.0-22.el7.x86_64
  libvirt-1.2.17-7.el7.x86_64
  

How reproducible:
100%

Steps to Reproduce:
1.cat lxc.xml:
<domain type='lxc' id='3211'>
  <name>test</name>
  <uuid>02ea2ce6-55c7-4c4b-aef2-cddf9edecc8f</uuid>
  <memory unit='KiB'>1048576</memory>
  <currentMemory unit='KiB'>1048576</currentMemory>
  <vcpu placement='static'>1</vcpu>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64'>exe</type>
    <init>/bin/sh</init>
  </os>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/libexec/libvirt_lxc</emulator>
    <filesystem type='mount' accessmode='passthrough'>
      <source dir='/'/>
      <target dir='/'/>
    </filesystem>
    <interface type='network'>
      <mac address='00:16:3e:54:f2:8c'/>
      <source network='default'/>
      <target dev='vnet0'/>
    </interface>
    <console type='pty' tty='/dev/pts/1'>
      <source path='/dev/pts/1'/>
      <target type='lxc' port='0'/>
      <alias name='console0'/>
    </console>
  </devices>
  <seclabel type='none' model='selinux'/>
</domain>

2. virsh -c lxc:/// define lxc.xml
3. virsh -c lxc:/// start lxc1
4. virsh -c lxc:/// dumpxml lxc1 > /tmp/a.xml
5. virt-xml-validate /tmp/a.xml

Additional:
It's a regression bug,but not very serious.
see:
https://bugzilla.redhat.com/show_bug.cgi?id=1028107