net: fill in MODULE_DESCRIPTION()s for net/sched

W=1 builds now warn if module is built without a MODULE_DESCRIPTION().
Add descriptions to the network schedulers.

Suggested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20240208164244.3818498-8-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>