[SCTP]: Remove sctp_add_cmd_sf wrapper bloat

With a was number of callsites sctp_add_cmd_sf wrapper bloats
kernel by some amount. Due to unlikely tracking allyesconfig,
with the initial result were around ~7kB (thus caught my
attention) while a non-debug config produced only ~2.3kB effect.

I (ij) proposed first a patch to uninline it but Vlad responded
with a patch that removed the only sctp_add_cmd call which is
wrapped by sctp_add_cmd_sf (I wasn't sure if I could do that).
I did minor cleanup to Vlad's patch.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>