net: net_{enable|disable}_timestamp() optimizations

Adopting atomic_try_cmpxchg() makes the code cleaner.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2073,13 +2073,10 @@ static DECLARE_WORK(netstamp_work, netstamp_clear);
 void net_enable_timestamp(void)
 {
 #ifdef CONFIG_JUMP_LABEL
-	int wanted;
+	int wanted = atomic_read(&netstamp_wanted);
 
-	while (1) {
-		wanted = atomic_read(&netstamp_wanted);
-		if (wanted <= 0)
-			break;
-		if (atomic_cmpxchg(&netstamp_wanted, wanted, wanted + 1) == wanted)
+	while (wanted > 0) {
+		if (atomic_try_cmpxchg(&netstamp_wanted, &wanted, wanted + 1))
 			return;
 	}
 	atomic_inc(&netstamp_needed_deferred);
@@ -2093,13 +2090,10 @@ EXPORT_SYMBOL(net_enable_timestamp);
 void net_disable_timestamp(void)
 {
 #ifdef CONFIG_JUMP_LABEL
-	int wanted;
+	int wanted = atomic_read(&netstamp_wanted);
 
-	while (1) {
-		wanted = atomic_read(&netstamp_wanted);
-		if (wanted <= 1)
-			break;
-		if (atomic_cmpxchg(&netstamp_wanted, wanted, wanted - 1) == wanted)
+	while (wanted > 1) {
+		if (atomic_try_cmpxchg(&netstamp_wanted, &wanted, wanted - 1))
 			return;
 	}
 	atomic_dec(&netstamp_needed_deferred);