wifi: Fixing Nits

Changes in the CL to fix bugs found while integrating
with framework:
1. Added IWifiApIface.setCountryCode()
Bug: 34682168
2. Fixed documentation nits in .hal files.
Bug: 34468218
3. Changed roaming state enum values.
Bug: 34715231
4. Added log for EBUSY in legacyErrorToString()
Bug: 34715469
5. Remove "-Wno-unused parameter" from Android.mk
Bug: 34611289
6. Remove the erroneous |onFailure| callback invocation in wifi.cpp.
7. Add null terminations to strings passed to legacy HAL API's
8. Remove unused |IWifiStaIface.stopDebugPacketFateMonitoring|.

Test: Compiles
Change-Id: If3a3e2f360a378c59dc56b8bbe3a0c6d400b3bd8