netconsole: selftest: add task name append testing

Add test coverage for the netconsole task name feature to the existing
sysdata selftest script. This extends the test infrastructure to verify
that task names are correctly appended when enabled and absent when
disabled.

The test validates that:
  - Task names appear in the expected format "taskname=<name>"
  - Task names are included when the feature is enabled
  - Task names are excluded when the feature is disabled
  - The feature works correctly alongside other sysdata fields like CPU

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>