bnxt_en: Add ethtool mac loopback self test (reapply).

bnxt_en: Add ethtool mac loopback self test (reapply).

The mac loopback self test operates in polling mode.  To support that,
we need to add functions to open and close the NIC half way.  The half
open mode allows the rings to operate without IRQ and NAPI.  We
use the XDP transmit function to send the loopback packet.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ Upstream commit f7dc1ea6c4c1f31371b7098d6fae0d49dc6cdff1 ]
Orabug: 27988326

Signed-off-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>
Reviewed-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>