net: print a notification on device rename

Currently it's done silently (from the kernel part), and thus it might be
hard to track the renames from logs.

Add a simple netdev_info() to notify the rename, but only in case the
previous name was valid.

CC: "David S. Miller" <[e-mail]>
CC: Eric Dumazet <[e-mail]>
CC: Vlad Yasevich <[e-mail]>
CC: stephen hemminger <[e-mail]>
CC: Jerry Chu <[e-mail]>
CC: Ben Hutchings <[e-mail]>
CC: David Laight <[e-mail]>
Signed-off-by: Veaceslav Falico <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/dev.c

···
 		return err;
 	}
 
+	if (oldname[0] && !strchr(oldname, '%'))
+		netdev_info(dev, "renamed from %s\n", oldname);
+
 	old_assign_type = dev->name_assign_type;
 	dev->name_assign_type = NET_NAME_RENAMED;