[DCCP]: Warn when discarding packet due to internal errors

This adds a (debug) warning message which is triggered whenever a packet is
discarded due to send failure.

It also adds a conditional, so that an interruption during dccp_wait_for_ccid
is not treated as a `BUG': the rationale is that interruptions are external,
whereas bug warnings are concerned with the internals.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

net/dccp/output.c

@@ -241,7 +241,7 @@ void dccp_write_xmit(struct sock *sk, int block)
 				break;
 			} else
 				err = dccp_wait_for_ccid(sk, skb);
-			if (err)
+			if (err && err != -EINTR)
 				DCCP_BUG("err=%d after dccp_wait_for_ccid", err);
 		}
 
@@ -267,8 +267,10 @@ void dccp_write_xmit(struct sock *sk, int block)
 			if (err)
 				DCCP_BUG("err=%d after ccid_hc_tx_packet_sent",
 					 err);
-		} else
+		} else {
+			dccp_pr_debug("packet discarded\n");
 			kfree(skb);
+		}
 	}
 }