[TASK] Refactor AP metrics response collection

[arnout]

Description

The AP metrics query/response flow requires sending the query to several radios, collecting the responses from the radios, and finally sending out all the responses in a single message.

#1231 implemented that, but it has a few shortcomings:

• MID is not stored;
• response is not properly checked against expected responses;
• if several BSSIDs are queried, there is one query per BSSID -> redundant messages;
• corner cases could be checked better;
• instead of collecting responses in structures, it might be better to construct a cmdu_tx directly;
• agent: backhaul_manager: fix test 4.7.5 #1388 introduced a special case for responses that are generated directly by the monitor, which means that a request with that "magic MID" will not work correctly.

[mariomaz]

Provided solution must consider also the cases in which AP Metrics Response message must be sent not as a response to a previous AP Metrics Query message, but when an internal event occurs; like when periodic reporting metrics interval has elapsed or when channel utilization crosses configured threshold value.

[VladyslavTupikin]

Plan for refactoring is:

1. handle_ap_metrics_query should just fill up expected_bssid vector and forward the query.
   -- save mid
   -- clear expected_bssid
   -- clear response (just do new message creation)

2. For certification 4.7.5 create 1 big ap metric query and send it to all slaves.
   -- save mid
   -- clear expected_bssid
   -- clear response (just do new creation)
   -- //UINT16_MAX should be changed on 0, remove comment above

3. For handle_slave_ap_metrics_response
   -- check received mid with saved:
   if (mid != saved_mid) {
   if (mid == 0)
   forward it to the controller;
   return;
   else
   drop;
   }
   -- create tlvs according to the information from cmdu_rx
   -- remove all useless structures

Commits:
1st create stuff from UML and modify handle_ap_metrics_query
2nd Modifying send_slave_ap_metric_query_message, also add condition if (mid != saved_mid)
3rd Change structures to the cmdu_tx in handle_slave_ap_metrics_response
4th Remove all structures

[VladyslavTupikin]

[arnout]

@mariomaz @RanRegev Please review the design posted by @VladyslavTupikin