net/failsafe: check code of allmulticast mode switch

net/failsafe: check code of allmulticast mode switch

rte_eth_allmulticast_enable()/rte_eth_allmulticast_disable() return
value was changed from void to int, so this patch modify usage
of these functions across net/failsafe according to new return type.

Try to keep all-multicast mode consistent across all active
devices in the case of failure.

Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>