net/enic: fix crash on MTU update with non-setup queues

net/enic: fix crash on MTU update with non-setup queues

The enic code called from rte_eth_dev_set_mtu() was assuming that the
Rx queues are already set up via a call to rte_eth_tx_queue_setup().
OVS calls rte_eth_dev_set_mtu() before rte_eth_rx_queue_setup() and
a null pointer was dereferenced.

Fixes: c3e09182bcd6 ("net/enic: support scatter Rx in MTU update")
Cc: stable@dpdk.org
Signed-off-by: John Daley <johndale@cisco.com>
Reviewed-by: Hyong Youb Kim <hyonkim@cisco.com>