net/enic: fix crash caused by changing MTU

net/enic: fix crash caused by changing MTU

Changing MTU after the device start causes a segfault in the Rx
handler. The MTU handler (enic_set_mtu) performs the following steps.
1. Stop NIC Rx
2. Change Rx handler '(struct rte_eth_dev)->rx_pkt_burst' to
   the dummy handler and sleep a while to quiesce
3. Re-allocate/initialize Rx structures
4. Change Rx handler back to the real handler
   (e.g. enic_noscatter_recv_pkts)

enic_set_mtu does not update the recently introduced fast-path pointer
'(struct rte_eth_fp_ops)->rx_pkt_burst'. Since rte_eth_rx_burst only
uses the fast-path pointer, it keeps invoking the real Rx handler, not
the dummy one set by (2). And, (3) causes a segfault in the real Rx
handler (e.g. dereferencing freed structures).

Fix the segfault by updating the fast-path pointer as well.

Fixes: c87d435a4d79 ("ethdev: copy fast-path API into separate structure")
Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
Reviewed-by: John Daley <johndale@cisco.com>