bnxt_en: Use NETIF_F_GRO_HW.

Advertise NETIF_F_GRO_HW in hw_features if hardware GRO is supported.
In bnxt_fix_features(), disable GRO_HW and LRO if current hardware
configuration does not allow it.  GRO_HW depends on GRO.  GRO_HW is
also mutually exclusive with LRO.  XDP setup will now rely on
bnxt_fix_features() to turn off aggregation.  During chip init, turn on
or off hardware GRO based on NETIF_F_GRO_HW in features flag.

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