sfc: VLAN filters must only be created if the firmware supports this.

If it is not supported we simply disable the feature.

For the feature to work we need firmware filter support for
OUTER_VID + LOC_MAC and for OUTER_VID + LOC_MAC_IG.
The low-latency firmware can match on OUTER_VID + LOC_MAC but not on
OUTER_VID + LOC_MAC_IG.
For the capture packet firmware it is the other way around.
Only the full-feature variant can match on both combinations.

Incorporates a fix by Andrew Rybchenko <Andrew.Rybchenko@oktetlabs.ru>
in the net_dev->[hw_]features handling.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>