[NET]: improve readability of dev_set_promiscuity() in net/core/dev.c

A trivial patch to improve the readability of dev_set_promiscuity()
in net/core/dev.c. New code does exactly the same thing as original
code.
Signed-off-by: David Chau <ddcc@mit.edu>
Signed-off-by: Domen Puncer <domen@coderock.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2089,10 +2089,11 @@ void dev_set_promiscuity(struct net_device *dev, int inc)
 {
 	unsigned short old_flags = dev->flags;
 
-	dev->flags |= IFF_PROMISC;
 	if ((dev->promiscuity += inc) == 0)
 		dev->flags &= ~IFF_PROMISC;
-	if (dev->flags ^ old_flags) {
+	else
+		dev->flags |= IFF_PROMISC;
+	if (dev->flags != old_flags) {
 		dev_mc_upload(dev);
 		printk(KERN_INFO "device %s %s promiscuous mode\n",
 		       dev->name, (dev->flags & IFF_PROMISC) ? "entered" :