[DCCP]: Use AF-independent rebuild_header routine

This fixes a nasty bug: dccp_send_reset() is called by both DCCPv4 and DCCPv6, but uses
inet_sk_rebuild_header() in each case. This leads to unpredictable and weird behaviour:
under some conditions, DCCPv6 Resets were sent, in other not.

The fix is to use the AF-independent rebuild_header routine.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/dccp/output.c

@@ -391,7 +391,7 @@ int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
 	 * FIXME: what if rebuild_header fails?
 	 * Should we be doing a rebuild_header here?
 	 */
-	int err = inet_sk_rebuild_header(sk);
+	int err = inet_csk(sk)->icsk_af_ops->rebuild_header(sk);
 
 	if (err != 0)
 		return err;