rte_eth_promiscuous_enable()/rte_eth_promiscuous_disable() return
value was changed from void to int, so modify usage of these
functions across lib/librte_kni according to new return type.
Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>