qcacld-3.0: Refine sys_process_mmh_msg()

There are currently a multitude of issues with sys_process_mmh_msg()
so update both the interface and the implementation to align with good
software engineering practices and the Linux Coding Style.

Change-Id: I76e53772dd72426cc4245756457e2a8140937571
CRs-Fixed: 2411714
6 files changed