network/netdev: generate persistent MAC address for batadv and bridge

This mostly reverts 489f01f806 and
deb2cfa4c6.

As now MACAddress=none is supported. So, users can still disable MAC
address assignment.

src/network/netdev/batadv.c

@@ -203,4 +203,5 @@ const NetDevVTable batadv_vtable = {
         .post_create = netdev_batadv_post_create,
         .create_type = NETDEV_CREATE_MASTER,
         .iftype = ARPHRD_ETHER,
+        .generate_mac = true,
 };

src/network/netdev/bridge.c

@@ -278,4 +278,5 @@ const NetDevVTable bridge_vtable = {
         .post_create = netdev_bridge_post_create,
         .create_type = NETDEV_CREATE_MASTER,
         .iftype = ARPHRD_ETHER,
+        .generate_mac = true,
 };