PYTHON-1714 Add c extension use to client metadata

Fix tests
	- `has_c` is a func!

Author: aclark4life

pymongo/pool_options.py

@@ -364,7 +364,7 @@ def __init__(
         #    },
         #    'platform': 'CPython 3.8.0|MyPlatform'
         # }
-        if has_c:
+        if has_c():
             self.__metadata["driver"]["name"] = "{}|{}".format(
                 self.__metadata["driver"]["name"],
                 "c",