[DCCP]: Simplified conditions due to use of enum:8 states

This reaps the benefit of the earlier patch, which changed the type of
CCID 3 states to use enums, in that many conditions are now simplified
and the number of possible (unexpected) values is greatly reduced.

In a few instances, this also allowed to simplify pre-conditions; where
care has been taken to retain logical equivalence.

[DCCP]: Introduce a consistent BUG/WARN message scheme

This refines the existing set of DCCP messages so that
 * BUG(), BUG_ON(), WARN_ON() have meaningful DCCP-specific counterparts
 * DCCP_CRIT (for severe warnings) is not rate-limited
 * DCCP_WARN() is introduced as rate-limited wrapper

Using these allows a faster and cleaner transition to their original
counterparts once the code has matured into a full DCCP implementation.

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 03bb829..c7aaa25 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -828,9 +828,7 @@
 	/* Step 1: If header checksum is incorrect, drop packet and return. */
 	if (dccp_v6_csum_finish(skb, &skb->nh.ipv6h->saddr,
 				     &skb->nh.ipv6h->daddr)) {
-		LIMIT_NETDEBUG(KERN_WARNING
-			       "%s: dropped packet with invalid checksum\n",
-			       __FUNCTION__);
+		DCCP_WARN("dropped packet with invalid checksum\n");
 		goto discard_it;
 	}