selftests: devlink_trap_l3_drops: Add test cases of irif and erif disabled

Add test cases to check that packets routed through disabled RIFs and
packets routed from disabled RIFs are dropped and devlink counters
increase when the action is trap.

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>