net/mrvl: fix mbuf to bpool lookup

net/mrvl: fix mbuf to bpool lookup

Since in DPDK 17.11 port type was changed from uint8_t to uint16_t
the MBUF_INVALID_PORT value became 0xffff but in mrvl_tx_pkt_burst()
when trying to lookup bpool using mbuf port, we check if the port
is invalid according to value 0xff. This causes segmentation fault.

Solution: since the valid port value cannot exceed RTE_MAX_ETHPORTS
(size of bpool lookup table) any other values consider as invalid so
the packet should be returned to DPDK pool.

Fixes: afb4d0d0bf91 ("net/mrvl: add Rx/Tx support")
Cc: stable@dpdk.org
Signed-off-by: Natalie Samsonov <nsamsono@marvell.com>