bnx2x: Use NETIF_F_GRO_HW.

Advertise NETIF_F_GRO_HW and turn on TPA_MODE_GRO when NETIF_F_GRO_HW
is set.  Disable NETIF_F_GRO_HW in bnx2x_fix_features() if the MTU
does not support TPA_MODE_GRO or GRO is not set.  bnx2x_change_mtu() also
needs to disable NETIF_F_GRO_HW if the MTU does not support it.

Original parameter disable_tpa will continue to disable LRO and GRO_HW.

Preserve the original behavior of enabling LRO by default.  User has
to run ethtool -K to explicitly enable GRO_HW.

Cc: Ariel Elior <Ariel.Elior@cavium.com>
Cc: everest-linux-l2@cavium.com
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Acked-by: Manish Chopra <manish.chopra@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>