Refactoring MONGO_METHOD calls in mongoclient.c and mongo.c

https://jira.mongodb.org/browse/PHP-820 and related sub-tasks
This is keeping the existing code after I split up the switch statement, so I really didn't add anything. I refactored the `MONGO_METHOD1` call, and I believe the macros that do argument stack pushing are the priority here (see my earlier PR comment).