change []'s to italic in docstring

inventory_provider/routes/poller.py

@@ -357,7 +357,8 @@ def interface_speeds(hostname=None):
 
     The response is a list of maximum speed information (in bits
     per second) for all known interfaces.
-    [speed <= 0 means the max interface speed can't be determined]
+
+    *speed <= 0 means the max interface speed can't be determined*
 
     .. asjson::
        inventory_provider.routes.poller.INTERFACE_SPEED_LIST_SCHEMA