qcacld-3.0: Refine the SME NAN public interface

Update the SME NAN public interface as follows:
1) Move the sme_nan_event() prototype to nan_api.h
2) Fully document the interfaces (not the implementations)
3) Utilize the new mac_handle_t abstraction
4) Clean up local coding style violations

Change-Id: I7ae6fff6e4a44570463383e9f6f50731fa594192
CRs-Fixed: 2335643
3 files changed