[SCTP] embedded sctp_addr: net-endian mirrors

Add sctp_chunk->source, sctp_sockaddr_entry->a, sctp_transport->ipaddr
and sctp_transport->saddr, maintain them as net-endian mirrors of
their host-endian counterparts.

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