[DCCP]: Miscellaneous code tidy-ups

This patch does not change code; it performs some trivial clean/tidy-ups:

  * removal of a `debug_prefix' string in favour of the
    already existing dccp_role(sk)

  * add documentation of structures and constants

  * separated out the cases for invalid packets (step 1
    of the packet validation)

  * removing duplicate statements

  * combining declaration & initialisation

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
index 2165b17..fc32617 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -318,7 +318,7 @@
 				       sizeof(struct dccp_hdr_reset);
 	struct sk_buff *skb;
 	struct flowi fl;
-	u64 seqno;
+	u64 seqno = 0;
 
 	if (rxdh->dccph_type == DCCP_PKT_RESET)
 		return;
@@ -345,13 +345,11 @@
 				DCCP_SKB_CB(rxskb)->dccpd_reset_code;
 
 	/* See "8.3.1. Abnormal Termination" in RFC 4340 */
-	seqno = 0;
 	if (DCCP_SKB_CB(rxskb)->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
 		dccp_set_seqno(&seqno, DCCP_SKB_CB(rxskb)->dccpd_ack_seq + 1);
 
 	dccp_hdr_set_seq(dh, seqno);
-	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb),
-			 DCCP_SKB_CB(rxskb)->dccpd_seq);
+	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), DCCP_SKB_CB(rxskb)->dccpd_seq);
 
 	dccp_csum_outgoing(skb);
 	dh->dccph_checksum = dccp_v6_csum_finish(skb, &rxskb->nh.ipv6h->saddr,