Avoid crash when LXC start fails with no interface target

If the <interface> device did not contain any <target>
element, LXC would crash on a NULL pointer if starting
the container failed
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/lxc/lxc_process.c

@@ -254,7 +254,8 @@ static void virLXCProcessCleanup(virLXCDriverPtr driver,
     for (i = 0 ; i < vm->def->nnets ; i++) {
         virDomainNetDefPtr iface = vm->def->nets[i];
         vport = virDomainNetGetActualVirtPortProfile(iface);
-        ignore_value(virNetDevSetOnline(iface->ifname, false));
+        if (iface->ifname)
+            ignore_value(virNetDevSetOnline(iface->ifname, false));
         if (vport && vport->virtPortType == VIR_NETDEV_VPORT_PROFILE_OPENVSWITCH)
             ignore_value(virNetDevOpenvswitchRemovePort(
                             virDomainNetGetActualBridgeName(iface),