mlxsw: Add layer 3 devlink-trap support

Add the trap IDs and trap group used to report layer 3 drops. Register
layer 3 packet traps and associated layer 3 trap group with devlink
during driver initialization.

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