dccp: Cleanup routines for feature negotiation

This inserts the required de-allocation routines for memory allocated by 
feature negotiation in the socket destructors, replacing dccp_feat_clean()
in one instance.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>

net/dccp/ipv6.c

@@ -302,6 +302,7 @@ done:
 
 static void dccp_v6_reqsk_destructor(struct request_sock *req)
 {
+	dccp_feat_list_purge(&dccp_rsk(req)->dreq_featneg);
 	if (inet6_rsk(req)->pktopts != NULL)
 		kfree_skb(inet6_rsk(req)->pktopts);
 }