net: ena: Extend customer metrics reporting support

ENA currently supports the following customer metrics:
- `bw_in_allowance_exceeded`
- `bw_out_allowance_exceeded`
- `conntrack_allowance_exceeded`
- `linklocal_allowance_exceeded`
- `pps_allowance_exceeded`

This patch adds a new metric named:
`conntrack_allowance_available`.

Information about these metrics is available in [1].

In addition, the interface between the driver and the
device has been upgraded to allow more flexibility and
expendability to additional metrics in the future.

[1]: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/monitoring-network-performance-ena.html#network-performance-metrics



Signed-off-by: Ron Beider <rbeider@amazon.com>
Signed-off-by: Shahar Itzko <itzko@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
Link: https://patch.msgid.link/20240909084704.13856-3-darinzon@amazon.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>