netdevsim: Explicitly register packet trap groups

Use the previously added API to explicitly register / unregister
supported packet trap groups. This is in preparation for future patches
that will enable drivers to pass additional group attributes, such as
associated policer identifier.

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