macvtap: fix the missing ret value of TUNSETQUEUE

Commit 441ac0fcaadc76ad09771812382345001dd2b813
(macvtap: Convert to using rtnl lock) forget to return what
macvtap_ioctl_set_queue() returns to its caller. This may break multiqueue API
by always falling through to TUNGETFEATURES.

Cc: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macvtap.c

@@ -1107,6 +1107,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
 		rtnl_lock();
 		ret = macvtap_ioctl_set_queue(file, u);
 		rtnl_unlock();
+		return ret;
 
 	case TUNGETFEATURES:
 		if (put_user(IFF_TAP | IFF_NO_PI | IFF_VNET_HDR |