The overcome instabilities in the RTT results add smoothing logic
to the reported results. In short, the smoothing logic tracks the
RTT average of each responder for a period of time, and in case
a new RTT results is found to be a spur, the tracked RTT average
is reported instead of the current RTT measurement.

Smooth logic debug configuration using iwl-dbg-cfg.ini:

- MVM_FTM_INITIATOR_ENABLE_SMOOTH: Set to 1 to enable smoothing logic
 (default=0).
- MVM_FTM_INITIATOR_SMOOTH_ALPHA: A value between 0 - 100, defining
  the weight of the current RTT results vs. the RTT average tracked
  based on the previous results. A value of 100 means use only the
  current RTT results.
- MVM_FTM_INITIATOR_SMOOTH_AGE_SEC: The maximal time in seconds in which
  the RTT average tracked based on previous results is considered valid.
- MVM_FTM_INITIATOR_SMOOTH_UNDERSHOOT: if the current RTT is positive
  and below the RTT average by at least this value, report the average
  RTT instead of the current one. In units of picoseconds.
- MVM_FTM_INITIATOR_SMOOTH_OVERSHOOT: if the current RTT is positive
  and above the RTT average by at least this value, report the average
  RTT instead of the current one. In units of picoseconds.
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200930161256.48a9cec2081b.Iaec1e29f738232adfe9e2ea8e9eb9b6ff0323ae1@changeidSigned-off-by: Luca Coelho <luciano.coelho@intel.com>