[NET]: Make netlink processing routines semi-synchronious (inspired by rtnl) v2

The code in netfilter/nfnetlink.c and in ./net/netlink/genetlink.c looks
like outdated copy/paste from rtnetlink.c. Push them into sync with the
original.

Changes from v1:
- deleted comment in nfnetlink_rcv_msg by request of Patrick McHardy

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 07ef5d2..3f1104d 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -22,22 +22,14 @@
 
 static DEFINE_MUTEX(genl_mutex); /* serialization of message processing */
 
-static void genl_lock(void)
+static inline void genl_lock(void)
 {
 	mutex_lock(&genl_mutex);
 }
 
-static int genl_trylock(void)
-{
-	return !mutex_trylock(&genl_mutex);
-}
-
-static void genl_unlock(void)
+static inline void genl_unlock(void)
 {
 	mutex_unlock(&genl_mutex);
-
-	if (genl_sock && genl_sock->sk_receive_queue.qlen)
-		genl_sock->sk_data_ready(genl_sock, 0);
 }
 
 #define GENL_FAM_TAB_SIZE	16
@@ -483,8 +475,7 @@
 	unsigned int qlen = 0;
 
 	do {
-		if (genl_trylock())
-			return;
+		genl_lock();
 		qlen = netlink_run_queue(sk, qlen, genl_rcv_msg);
 		genl_unlock();
 	} while (qlen && genl_sock && genl_sock->sk_receive_queue.qlen);