[SCTP]: Switch sctp_assoc_is_match to net-endian.

Along with it, statics in input.c that end up calling it
(__sctp_lookup_association, sctp_lookup_association,
__sctp_rcv_init_lookup, __sctp_rcv_lookup).  Callers
are adjusted.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>