net: Remove duplicated midx check against 0

Check midx against 0 is always equal to check midx against sk_bound_dev_if
when sk_bound_dev_if is known not equal to 0 in these case.
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_sockglue.c

@@ -1124,8 +1124,7 @@ static int do_ip_setsockopt(struct sock *sk, int level, int optname,
 		dev_put(dev);
 
 		err = -EINVAL;
-		if (sk->sk_bound_dev_if &&
-		    (!midx || midx != sk->sk_bound_dev_if))
+		if (sk->sk_bound_dev_if && midx != sk->sk_bound_dev_if)
 			break;
 
 		inet->uc_index = ifindex;
@@ -1189,7 +1188,7 @@ static int do_ip_setsockopt(struct sock *sk, int level, int optname,
 		err = -EINVAL;
 		if (sk->sk_bound_dev_if &&
 		    mreq.imr_ifindex != sk->sk_bound_dev_if &&
-		    (!midx || midx != sk->sk_bound_dev_if))
+		    midx != sk->sk_bound_dev_if)
 			break;
 
 		inet->mc_index = mreq.imr_ifindex;