netdev-dpdk: Disable net/tap Tx L4 checksum offloads.

As reported by Ales when doing some OVN integration tests with OVS 3.2,
net/tap has broken L4 checksum offloads.

Fixes are pending on DPDK side.
Until they get in a LTS release used by OVS, disable those Tx offloads.

Acked-by: Eelco Chaudron <echaudro@redhat.com>
Signed-off-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

lib/netdev-dpdk.c

@@ -1312,6 +1312,16 @@ dpdk_eth_dev_init(struct netdev_dpdk *dev)
         dev->hw_ol_features &= ~NETDEV_RX_HW_SCATTER;
     }
 
+    if (!strcmp(info.driver_name, "net_tap")) {
+        /* FIXME: L4 checksum offloading is broken in DPDK net/tap driver.
+         * This workaround can be removed once the fix makes it to a DPDK
+         * LTS release used by OVS. */
+        VLOG_INFO("%s: disabled Tx L4 checksum offloads for a net/tap port.",
+                  netdev_get_name(&dev->up));
+        info.tx_offload_capa &= ~RTE_ETH_TX_OFFLOAD_UDP_CKSUM;
+        info.tx_offload_capa &= ~RTE_ETH_TX_OFFLOAD_TCP_CKSUM;
+    }
+
     if (info.tx_offload_capa & RTE_ETH_TX_OFFLOAD_IPV4_CKSUM) {
         dev->hw_ol_features |= NETDEV_TX_IPV4_CKSUM_OFFLOAD;
     } else {