devlink: Only pass packet trap group identifier in trap structure

Packet trap groups are now explicitly registered by drivers and not
implicitly registered when the packet traps are registered. Therefore,
there is no need to encode entire group structure the trap is associated
with inside the trap structure.

Instead, only pass the group identifier. Refer to it as initial group
identifier, as future patches will allow user space to move traps
between groups.

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