net/nfb: remove resources when port is closed

The rte_eth_dev_close() function now handles freeing resources for
devices (e.g., mac_addrs).  To conform with the new close() behaviour we
are asserting the RTE_ETH_DEV_CLOSE_REMOVE flag so that
rte_eth_dev_close() releases all device level dynamic memory.

Signed-off-by: Rastislav Cernay <cernay@netcope.com>
Reviewed-by: Xiaolong Ye <xiaolong.ye@intel.com>
Acked-by: Jan Remes <remes@netcope.com>