qcacmn: Refine the Link Layer Stats Unified API

There are multiple issues with the Link Layer Stats Unified API:
- struct ll_stats_clear_params and struct ll_stats_get_params both
  incorrectly use the identifier "sta_id" to refer to a vdev_id.
- struct ll_stats_set_params has an unused "sta_id" field.
- Functions wmi_unified_process_ll_stats_clear_cmd() and
  wmi_unified_process_ll_stats_get_cmd() pass the MAC address as a
  separate parameter rather than adhering to the commonly used
  unified signature: func(handle, param).
- Not all of the functions and data structures are correctly protected
  by the WLAN_FEATURE_LINK_LAYER_STATS feature flag.

Refine the Link Layer Stats Unified API to address these issues.

This is co-dependent with Ifd7c8de2358121dae4752525ff57021a32be85d3
("qcacld-3.0: Use the refined Link Layer Stats Unified API").

Change-Id: Ifdc1fada55a559f3b3d0837ec20cceb653c45c40
CRs-Fixed: 2409293
5 files changed