Emit aggregate and per device metrics for network devices:
 - Move NetDeviceMetrics from logger to Net module.
 - Use NET_DEV_METRICS_PVT instead of adding an entry of
   NetDeviceMetrics in Net so that metrics can be flushed
   even from signal handlers.

Note: this is part 1 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Use individual instance of metrics instead of the METRICS.net.
Since we do not use METRIC.net, modify report_net_event_fail to
use self.metrics.

Note: this is part 2 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Update CHANGELOGS to notify that Firecracker now emits
per net device metrics.

Note: this is part 3 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Create a unit test that allocates 19 NetDeviceMetrics
(19 because it is the max number of irqs we have for
net devices), update and verify a metric.

Note: this is part 4 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Use RwLock to make accessing Metrics threadsafe.
Use better name to allocate NetDeviceMetrics

Note: this is part 5 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

With Vec based approach, "net0" is metrics for the 1st net device
created. However, if devices are not created in the same order all
the time, the first device created could either be eth0 or eth1 and
then net0 could sometimes point to eth0 and sometimes to eth1 which
doesn't help with analysing the metrics.
So, use Map instead of Vec to provide more clarity on which interface
the metrics actually belongs to.
Also, instead of net0 name the metrics json object as net_$iface_id
e.g. net_eth0 or net_eth1 which should help in better analysis.
Use "net_$iface_id" for the metrics name instead of "net_$tap_name" to
be consistent with the net endpoint "/network-interfaces/{iface_id}"

Note: this is part 6 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Use proper convention of lower case for macros.
Make CHANHELOG less verbose.

Note: this is part 7 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

NetMetricsSerializer naming was confusing because its not a
Serializer in serde's sense (it implements Serialize, not Serializer).
So give it to a better name.

Note: this is part 8 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

NetDeviceMetrics was moved from logger which needed the new()
because default didn't provide the const implementation that
FirecrackerMetrics::new() needed. But since that is not a requirement
anymore we rely on default to provide 0 initialized NetDeviceMetrics.

NetMetricsSerializeProxy doesn't have any fields and so there is no
need to define new() for it.

Note: this is part 9 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Better implementation for flush_metrics as suggested in feedback.

Note: this is part 10 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Make sure there is no breaking change for NetDeviceMetrics.
Add random number of net devices and validate that values of
"net" are aggregate of all "net_{iface_id}".

Note: this is part 11 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>

Use Arc for NetDeviceMetrics since this allows us to store
NetDeviceMetrics directly inside Net and get rid of the
net_metrics! macro.
Also, use better name for net metrics.

Note: this is part 12 of 12 commits to add per net device metrics.

Signed-off-by: Sudan Landge <sudanl@amazon.com>