[NET]: Conditionally use bh_lock_sock_nested in sk_receive_skb

Spotted by Ian McDonald, tentatively fixed by Gerrit Renker:

http://www.mail-archive.com/dccp%40vger.kernel.org/msg00599.html

Rewritten not to unroll sk_receive_skb, in the common case, i.e. no lock
debugging, its optimized away.

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
index a20eb71..7114bef 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -899,7 +899,7 @@
 		goto discard_and_relse;
 	nf_reset(skb);
 
-	return sk_receive_skb(sk, skb);
+	return sk_receive_skb(sk, skb, 1);
 
 no_dccp_socket:
 	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))