bnxt_en: convert to xdp_do_flush

The xdp_do_flush_map function has been replaced with the more general
xdp_do_flush().

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