[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/proto.c b/net/dccp/proto.c
index 9c9c08c..0225bda 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -452,9 +452,8 @@
 static int do_dccp_setsockopt(struct sock *sk, int level, int optname,
 		char __user *optval, int optlen)
 {
-	struct dccp_sock *dp;
-	int err;
-	int val;
+	struct dccp_sock *dp = dccp_sk(sk);
+	int val, err = 0;
 
 	if (optlen < sizeof(int))
 		return -EINVAL;
@@ -466,9 +465,6 @@
 		return dccp_setsockopt_service(sk, val, optval, optlen);
 
 	lock_sock(sk);
-	dp = dccp_sk(sk);
-	err = 0;
-
 	switch (optname) {
 	case DCCP_SOCKOPT_PACKET_SIZE:
 		dp->dccps_packet_size = val;