[sysmon] Move net_io_counters collection to separate function

More network metrics will be added soon.

BUG=chromium:698056
TEST=None

Change-Id: I0a15a678621b0d9b63c82a5083808ff1751bc818
Reviewed-on: https://chromium-review.googlesource.com/448806
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
diff --git a/scripts/sysmon/system_metrics.py b/scripts/sysmon/system_metrics.py
index e9453ff..eeccdf5 100644
--- a/scripts/sysmon/system_metrics.py
+++ b/scripts/sysmon/system_metrics.py
@@ -218,6 +218,12 @@
 
 
 def collect_net_info():
+  """Collect network metrics."""
+  _collect_net_io_counters()
+
+
+def _collect_net_io_counters():
+  """Collect metrics for network IO counters."""
   metric_counter_names = [
       (_net_up_metric, 'bytes_sent'),
       (_net_down_metric, 'bytes_recv'),