net/sfc: fix reported promiscuous/multicast mode

Requested promiscuous or all-multicast mode may be dropped on port
start if FW denies to enable it (e.g. because of no permission
in the case of VF). Return applied value on get.

Fixes: f5258439ee5d ("net/sfc: avoid failure on port start if Rx mode is rejected")
Cc: stable@dpdk.org
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>