net: rmnet: add missing module alias

In the current rmnet code, there is no module alias.
So, RTNL couldn't load rmnet module automatically.

Test commands:
    ip link add dummy0 type dummy
    modprobe -rv rmnet
    ip link add rmnet0 link dummy0 type rmnet  mux_id 1
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c

@@ -475,4 +475,5 @@ static void __exit rmnet_exit(void)
 
 module_init(rmnet_init)
 module_exit(rmnet_exit)
+MODULE_ALIAS_RTNL_LINK("rmnet");
 MODULE_LICENSE("GPL v2");