bnxt_en: Workaround Nitro A0 RX hardware bug (part 4).

Allocate special vnic for dropping packets not matching the RX filters.
First vnic is for normal RX packets and the driver will drop all
packets on the 2nd vnic.

Signed-off-by: Prashant Sreedharan <prashant.sreedharan@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>