[SCTP]: Fix multihomed connection failures on 64-bit systems.

Avoid the use of sizeof() and pointer arithmetic to get to the end
of sctp_cookie structure. Instead use the last element peer_init which
is a zero-sized array as the offset.

net/sctp/associola.c

@@ -1195,7 +1195,7 @@ int sctp_assoc_set_bind_addr_from_cookie(struct sctp_association *asoc,
 {
 	int var_size2 = ntohs(cookie->peer_init->chunk_hdr.length);
 	int var_size3 = cookie->raw_addr_list_len;
-	__u8 *raw = (__u8 *)cookie + sizeof(struct sctp_cookie) + var_size2;
+	__u8 *raw = (__u8 *)cookie->peer_init + var_size2;
 
 	return sctp_raw_to_bind_addrs(&asoc->base.bind_addr, raw, var_size3,
 				      asoc->ep->base.bind_addr.port, gfp);