mlxsw: spectrum: Add BGP trap

Add a trap for BGP protocol that was previously trapped by the generic trap
for IP2ME. This trap will allow us to have better control (over priority
and rate) of the traffic.

Signed-off-by: Nogah Frankel <nogahf@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>