[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/core/sock.c b/net/core/sock.c
index 32ff1c5..ab8fafa 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -270,7 +270,7 @@
 }
 EXPORT_SYMBOL(sock_queue_rcv_skb);
 
-int sk_receive_skb(struct sock *sk, struct sk_buff *skb)
+int sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested)
 {
 	int rc = NET_RX_SUCCESS;
 
@@ -279,7 +279,10 @@
 
 	skb->dev = NULL;
 
-	bh_lock_sock(sk);
+	if (nested)
+		bh_lock_sock_nested(sk);
+	else
+		bh_lock_sock(sk);
 	if (!sock_owned_by_user(sk)) {
 		/*
 		 * trylock + unlock semantics: