Change log level for 'loading devices' message (#20721)

The 'Loading [wireless] devices from Mikrotik ([ip address])' message
is incredibly spammy at the info log level, such that in the last 24
hours on my installation, that log message has appeared 6732 times,
versus 70 for every other log message. I've moved this message to the
debug log level as I don't believe it adds anything at the info level,
and makes it harder to diagnose other problems.

homeassistant/components/device_tracker/mikrotik.py

@@ -174,7 +174,7 @@ class MikrotikScanner(DeviceScanner):
             else:
                 devices_tracker = 'ip'
 
-        _LOGGER.info(
+        _LOGGER.debug(
             "Loading %s devices from Mikrotik (%s) ...",
             devices_tracker, self.host)