Revert "net-packet: fix race in packet_set_ring on PACKET_RESERVE"

This reverts commit ccf7bb73.

CVE-2017-1000111
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/packet/af_packet.c

@@ -3622,19 +3622,14 @@ packet_setsockopt(struct socket *sock, int level, int optname, char __user *optv
 
 		if (optlen != sizeof(val))
 			return -EINVAL;
+		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec)
+			return -EBUSY;
 		if (copy_from_user(&val, optval, sizeof(val)))
 			return -EFAULT;
 		if (val > INT_MAX)
 			return -EINVAL;
-		lock_sock(sk);
-		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec)
-			ret = -EBUSY;
-		else {
-			po->tp_reserve = val;
-			ret = 0;
-		}
-		release_sock(sk);
-		return ret;
+		po->tp_reserve = val;
+		return 0;
 	}
 	case PACKET_LOSS:
 	{