[SCTP]: Annotate ->dst_saddr()

switched to taking a pointer to net-endian sctp_addr
and a net-endian port number.  Instances and callers
adjusted; interestingly enough, the only calls are
direct calls of specific instances - the method is not
used at all.

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