bnxt: adding bnxt_xdp_build_skb to build skb from multibuffer xdp_buff

Since we have an xdp_buff with frags there needs to be a way to
convert that into a valid sk_buff in the event that XDP_PASS is
the resulting operation.  This adds a new rx_skb_func when the
netdev has an MTU that prevents the packets from sitting in a
single page.

This also make sure that GRO/LRO stay disabled even when using
the aggregation ring for large buffers.

v3: Use BNXT_PAGE_MODE_BUF_SIZE for build_skb

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