sctp: use read_lock_bh in sctp_eps_seq_show

This patch is to use read_lock_bh instead of local_bh_disable
and read_lock in sctp_eps_seq_show.

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