Ignore invalid output from docker stats command

[Junchao-Mellanox]

Why I did this

We found some error in syslog:

2025 Dec 10 22:42:06.221428 sonic ERR memory_threshold_check: Failed to parse memory usage for "{'CPU%': '--', 'MEM%': '--', 'MEM_BYTES': '0', 'MEM_LIMIT_BYTES': '0', 'NAME': '--', 'PIDS': '--'}": could not convert string to float: '--'
2025 Dec 10 22:42:06.221527 sonic ERR memory_threshold_check: Failure occurred could not convert string to float: '--'

The error is statistical. The flow is as below:

1. procdockerstatsd calls "docker stats" command periodically, parse the output and store to STATE DB
2. memory_threshold_check which is called by monit service, handles the data in STATE DB and check the memory usage

After reviewing sonic code and docker code, I found that sonic would never generate a data with NAME=--; while docker might do so. Docker might generate such invalid output in a flow like this:

1. user issues "docker stats -a --no-stream --format json" command
2. docker CLI sends a command to docker engine for all existing containers: container a, b, c and so on
   3. other user removes container a
3. docker engine starts to handle the command and find container a is no longer there, so it returns empty stats data
4. docker CLI finds the stats data for docker a in empty and fill the data with "--"

For detailed docker code, please check:
https://github.com/docker/cli/blob/93fa57bbcd08f2f5be7f6cf22f4273a2b5a49e71/cli/command/container/formatter_stats.go#L25
https://github.com/docker/cli/blob/93fa57bbcd08f2f5be7f6cf22f4273a2b5a49e71/cli/command/container/formatter_stats.go#L169

This PR is to fix the issue

How I did this

procdockerstatsd should check the command output and ignore invalid value:

1. if the name is empty of "--", ignore the output
2. log a warning message to syslog

How I test this

Manual test

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mssonicbld]

/azp run

[qiluo-msft]

thanks for this bugfix!

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mssonicbld]

Cherry-pick PR to 202511: #341