bnxt_en: Use page frag RX buffers for better software GRO performance

If NETIF_F_GRO_HW is disabled, the existing driver code uses kmalloc'ed
data for RX buffers.  This causes inefficient SW GRO performance
because the GRO data is merged using the less efficient frag_list.
Use netdev_alloc_frag() and friends instead so that GRO data can be
merged into skb_shinfo(skb)->frags for better performance.

[Use skb_free_frag() - Vikas Gupta]

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Reviewed-by: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: Vikas Gupta <vikas.gupta@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>