bnx2x: Fix VLANs null-pointer for 57710, 57711

bnx2x: Fix VLANs null-pointer for 57710, 57711

Commit 05cc5a39ddb7 "bnx2x: add vlan filtering offload" introduced
a regression in regard for vlans for 57710, 57711 adapters -
Loading 8021q module on a machine with such an adapter would cause
a null pointer dereference, as the driver mistakenly publishes it
has capabilities for vlan CTAG filtering.

Reported-by: Otto Sabart <[email protected]>
Signed-off-by: Yuval Mintz <[email protected]>
Signed-off-by: Ariel Elior <[email protected]>
Signed-off-by: David S. Miller <[email protected]>