sctp: Fix lock recursion in sctp_swap_inpcb_for_listen()

After commit bd4a39cc93d9 we now hold the global inp info lock across
the call to sctp_swap_inpcb_for_listen(), which attempts to acquire it
again. Since sctp_swap_inpcb_for_listen()'s sole caller is
sctp_listen(), we can simply change it to not try to acquire the lock.

Reported by: syzbot+a76b19ea2f8e1190c451@syzkaller.appspotmail.com
Reported by: syzbot+a1b6cef257ad145b7187@syzkaller.appspotmail.com
Reviewed by: tuexen
Fixes: bd4a39cc93d9 ("socket: Properly interlock when transitioning to a listening socket")
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31878