bnxt_en: Workaround Nitro A0 hardware RX bug (part 3).

Allocate napi for special vnic, packets arriving on this
napi will simply be dropped and the buffers will be replenished back
to the HW.

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