DPDK: Fix for vhost0 MTU not getting set

After an agent soft reset, vif 0 gets deleted and added back. But due to
a timing issue, before it gets added back, the vhost0 MTU notification
used to come resulting in MTU not getting set (Since vif is not added
yet). Fix is to query the MTU from PMD during vif 0 addition.

Change-Id: I262f2e62cbd390b3c8bae2bdc777fc1ac4249886
Closes-Bug: 1795839

dpdk/vr_dpdk_interface.c

@@ -735,6 +735,7 @@ dpdk_fabric_if_add(struct vr_interface *vif)
 {
     int ret;
     uint16_t port_id, ports_num;
+    uint16_t mtu;
     struct rte_pci_addr pci_address;
     struct vr_dpdk_ethdev *ethdev;
     struct ether_addr mac_addr;
@@ -792,6 +793,18 @@ dpdk_fabric_if_add(struct vr_interface *vif)
                 MAC_VALUE(mac_addr.addr_bytes), MAC_VALUE(vif->vif_mac));
     }
 
+    if (rte_eth_dev_get_mtu(port_id, &mtu) == 0 && mtu > 0) {
+         /* Ethernet header size */
+         mtu += sizeof(struct vr_eth);
+         if (vr_dpdk.vlan_tag != VLAN_ID_INVALID) {
+             /* 802.1q header size */
+             mtu += sizeof(uint32_t);
+         }
+         vif->vif_mtu = mtu;
+         if (vif->vif_bridge)
+             vif->vif_bridge->vif_mtu = mtu;
+    }
+
     ethdev = &vr_dpdk.ethdevs[port_id];
     if (ethdev->ethdev_ptr != NULL) {
         RTE_LOG(ERR, VROUTER, "    error adding eth dev %s: already added\n",