bnxt: set xdp_buff pfmemalloc flag if needed

Set the pfmemaloc flag in the xdp buff so that this can be
copied to the skb if needed for an XDP_PASS action.

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>