net/enic: fix the MTU handler to rely on max packet length

net/enic: fix the MTU handler to rely on max packet length

The RQ setup functions (enic_alloc_rq and enic_alloc_rx_queue_mbufs)
have changed to rely on max_rx_pkt_len to determine the use of scatter
and buffer size. But, the MTU handler only updates ethdev's MTU
value. So make it update max_rx_pkt_len as well. Other PMDs also
update both mtu and max_rx_pkt_len in their MTU handlers.

Also the condition for taking a short cut (scatter is disabled) in the
MTU handler is wrong. Even when scatter is disabled, a change in
max_rx_pkt_len may affect the buffer size posted to the NIC. So remove
that condition.

Finally, fix a comment and a warning message condition.

Fixes: 422ba91716a7 ("net/enic: heed the requested max Rx packet size")

Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
Reviewed-by: John Daley <johndale@cisco.com>
Reviewed-by: Aaron Conole <aconole@redhat.com>