netdev-dpdk: Fix failure to configure flow control at netdev-init.

This patch backports the commit from the latest OVS master to OVS-2.7.

Configuring flow control at ixgbe netdev-init is throwing error in port
start.
For eg: without this fix, user cannot configure flow control on ixgbe dpdk
port as below,

"
    ovs-vsctl add-port br0 dpdk0 -- set Interface dpdk0 type=dpdk \
        options:dpdk-devargs=0000:05:00.1 options:rx-flow-ctrl=true
"

Instead,  it must be configured as two different commands,

"
    ovs-vsctl add-port br0 dpdk0 -- set Interface dpdk0 type=dpdk \
               options:dpdk-devargs=0000:05:00.1
    ovs-vsctl set Interface dpdk0 options:rx-flow-ctrl=true
"

The DPDK ixgbe driver is now validating all the 'rte_eth_fc_conf' fields before
trying to configuring the dpdk ethdev. Hence OVS can no longer set the
'dont care' fields to just '0' as before. This commit make sure all the
'rte_eth_fc_conf' fields are populated with default values before the dev
init.
Also to avoid read error on unsupported ports, the flow control parameters
are now read only when user is trying to configure/update it.

Signed-off-by: Sugesh Chandran <sugesh.chandran@intel.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

lib/netdev-dpdk.c

@@ -830,14 +830,6 @@ dpdk_eth_dev_init(struct netdev_dpdk *dev)
 
     mbp_priv = rte_mempool_get_priv(dev->dpdk_mp->mp);
     dev->buf_size = mbp_priv->mbuf_data_room_size - RTE_PKTMBUF_HEADROOM;
-
-    /* Get the Flow control configuration for DPDK-ETH */
-    diag = rte_eth_dev_flow_ctrl_get(dev->port_id, &dev->fc_conf);
-    if (diag) {
-        VLOG_DBG("cannot get flow control parameters on port=%d, err=%d",
-                 dev->port_id, diag);
-    }
-
     return 0;
 }
 
@@ -1306,6 +1298,11 @@ netdev_dpdk_set_config(struct netdev *netdev, const struct smap *args,
 
     fc_mode = fc_mode_set[tx_fc_en][rx_fc_en];
     if (dev->fc_conf.mode != fc_mode || autoneg != dev->fc_conf.autoneg) {
+        err = rte_eth_dev_flow_ctrl_get(dev->port_id, &dev->fc_conf);
+        if (err) {
+            VLOG_WARN("Cannot get flow control parameters on port "
+                "%"PRIu16", err=%d", dev->port_id, err);
+        }
         dev->fc_conf.mode = fc_mode;
         dev->fc_conf.autoneg = autoneg;
         dpdk_eth_flow_ctrl_setup(dev);