Unify naming convention in apexd codebase

* Functions are named in CamelCase;
* Variables are named in snake_case;
* Constants are named in kCamelCase;

Hopefully, eventually we will be able to enforce this, but for the time
being let's manually unify it, which should make it easier to follow it
in the future cls.

Test: presubmit
Bug: 134388083
Change-Id: Ied83f6e60e84255aa450627169fbcee90a6491aa
6 files changed