Changes

s1gw_metrics: make exometer_report_statsd less verbose

When running osmo-s1gw with {logger_level, debug}, this module clogs
the logging output with dozens of "Report metric ..." lines.  This
makes debugging osmo-s1gw harder, so let's force it to use info.

Change-Id: I317680252d052f6435d870d27ca51514ca5f0c09