tun: Return -EINVAL if neither IFF_TUN nor IFF_TAP is set.

After commit 2b980dbd77d229eb60588802162c9659726b11f4
("lsm: Add hooks to the TUN driver") tun_set_iff doesn't
return -EINVAL though neither IFF_TUN nor IFF_TAP is set.

Signed-off-by: Kusanagi Kouichi <[e-mail]>
Reviewed-by: Paul Moore <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/tun.c

···
 		char *name;
 		unsigned long flags = 0;
 
-		err = -EINVAL;
-
 		if (!capable(CAP_NET_ADMIN))
 			return -EPERM;
 		err = security_tun_dev_create();
···
 			flags |= TUN_TAP_DEV;
 			name = "tap%d";
 		} else
-			goto failed;
+			return -EINVAL;
 
 		if (*ifr->ifr_name)
 			name = ifr->ifr_name;