net: sched: Fill in MODULE_DESCRIPTION for act_gate

net: sched: Fill in MODULE_DESCRIPTION for act_gate

W=1 builds now warn if module is built without a MODULE_DESCRIPTION().

Gate is the only TC action that is lacking such description.
Fill MODULE_DESCRIPTION for Gate TC ACTION.

Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Link: https://lore.kernel.org/r/20231027155045.46291-2-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>