net/octeontx2: fix packet type get overflow

The function `rte_eth_dev_get_supported_ptypes` expects the underlying
ethernet device to return array of supported ptypes. The ethernet device
needs to set `RTE_PTYPE_UNKNOWN` as the last element which signifies
thats its the end of the ptype array.
Else the function `rte_eth_dev_get_supported_ptypes` might overflow.

Fixes: 6e892eabce11 ("net/octeontx2: support packet type")
Cc: stable@dpdk.org
Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>