r8169: disable TSO on a single version of RTL8168c to fix performance

During performance testing, I found that one of my r8169 NICs suffered
a major performance loss, a 8168c model.

Running netperf's TCP_STREAM test didn't return the expected
throughput of > 900 Mb/s, but rather only about 22 Mb/s.  Strange
enough, running the TCP_MAERTS and UDP_STREAM tests all returned with
throughput > 900 Mb/s, as did TCP_STREAM with the other r8169 NICs I can
test (either one of 8169s, 8168e, 8168f).

Bisecting turned up commit 93681cd7,
"r8169: enable HW csum and TSO" as the culprit.

I added my 8168c version, RTL_GIGA_MAC_VER_22, to the code
special-casing the 8168evl as per the patch below.  This fixed the
performance problem for me.

Fixes: 93681cd7 ("r8169: enable HW csum and TSO")
Signed-off-by: Corinna Vinschen <vinschen@redhat.com>
Reviewed-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169_main.c

@@ -7179,8 +7179,11 @@ static int rtl_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 		dev->gso_max_segs = RTL_GSO_MAX_SEGS_V1;
 	}
 
-	/* RTL8168e-vl has a HW issue with TSO */
-	if (tp->mac_version == RTL_GIGA_MAC_VER_34) {
+	/* RTL8168e-vl and one RTL8168c variant are known to have a
+	 * HW issue with TSO.
+	 */
+	if (tp->mac_version == RTL_GIGA_MAC_VER_34 ||
+	    tp->mac_version == RTL_GIGA_MAC_VER_22) {
 		dev->vlan_features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
 		dev->hw_features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);
 		dev->features &= ~(NETIF_F_ALL_TSO | NETIF_F_SG);