mlxsw: Simplify traps creation

The Host Trap Group Table (HTGT) register configures trap groups, which
are populated with trap IDs using the Host PacKet Trap (HPKT) register.
However, a trap ID can only be present inside one trap group (the last
configured).

Instead of passing both the trap group and ID for the function that
packs HPKT, pass only the trap ID and derive from it the trap group.

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>