sctp: consolidate local_bh_disable/enable + spin_lock/unlock to _bh variant

local_bh_disable() + spin_lock() is equivalent to spin_lock_bh(), same for
the unlock/enable case, so replace the calls by the appropriate wrappers.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>