Silently ignore MAC in NetworkLoadConfig

Libvirt's RPMs have been adding it to networks which don't support it.

https://bugzilla.redhat.com/show_bug.cgi?id=1156367

src/conf/network_conf.c

@@ -3144,6 +3144,10 @@ virNetworkObjPtr virNetworkLoadConfig(virNetworkObjListPtr nets,
          */
         if (virNetworkSetBridgeName(nets, def, 0))
             goto error;
+    } else {
+        /* Throw away MAC address for other forward types,
+         * which could have been generated by older libvirt RPMs */
+        def->mac_specified = false;
     }
 
     if (!(net = virNetworkAssignDef(nets, def, false)))