network: honor mtu setting when creating network

This resolves: https://bugzilla.redhat.com/1224348

src/network/bridge_driver.c

@@ -2301,7 +2301,7 @@ networkStartNetworkVirtual(virNetworkDriverStatePtr driver,
         if (virNetDevTapCreateInBridgePort(network->def->bridge,
                                            &macTapIfName, &network->def->mac,
                                            NULL, NULL, &tapfd, 1, NULL, NULL,
-                                           0, NULL,
+                                           network->def->mtu, NULL,
                                            VIR_NETDEV_TAP_CREATE_USE_MAC_FOR_BRIDGE |
                                            VIR_NETDEV_TAP_CREATE_IFUP |
                                            VIR_NETDEV_TAP_CREATE_PERSIST) < 0) {