net: Remove likely from l3mdev_master_ifindex_by_index

The likely() annotation in l3mdev_master_ifindex_by_index() has been
found to be incorrect 100% of the time in real-world workloads (e.g.,
web servers).

Annotated branches shows the following in these servers:

	correct incorrect  %        Function                  File              Line
	      0 169053813 100 l3mdev_master_ifindex_by_index l3mdev.h             81

This is happening because l3mdev_master_ifindex_by_index() is called
from __inet_check_established(), which calls
l3mdev_master_ifindex_by_index() passing the socked bounded interface.

	l3mdev_master_ifindex_by_index(net, sk->sk_bound_dev_if);

Since most sockets are not going to be bound to a network device,
the likely() is giving the wrong assumption.

Remove the likely() annotation to ensure more accurate branch
prediction.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20241008163205.3939629-1-leitao@debian.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/l3mdev.h

@@ -78,7 +78,7 @@ static inline int l3mdev_master_ifindex_by_index(struct net *net, int ifindex)
 	struct net_device *dev;
 	int rc = 0;
 
-	if (likely(ifindex)) {
+	if (ifindex) {
 		rcu_read_lock();
 
 		dev = dev_get_by_index_rcu(net, ifindex);