sctp: remove the local_bh_disable/enable in sctp_endpoint_lookup_assoc

sctp_endpoint_lookup_assoc is called in the protection of sock lock
there is no need to call local_bh_disable in this function. so remove
them.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>