mlxsw: reg: Add FDB action to forward to router

Incoming packets are directed to the router when they match an FDB
entry with action forward to IP router.

Add this action, which was mistakenly named "TRAP".

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>