Receive uplink RSSI, calculate bandwidth congestion and packet rate

[gemenerik]

🚀 Features

Refactor link quality callback to contain signal health obj with additional signal health information:

• Uplink RSSI parsed from ack
• Bandwidth congestion calculated using null packet ratio
• Packet rate

📝 To-do

• CF link C++ uses a different calculation for link quality, investigate if we can unify this.
• Need to better integrate with Introduce Link Statistics and Latency Measurement #477, the signal health callback can probably be routed into LinkStatistics.
• Review naming for better clarity. Link statistics, link quality, and signal health can be easily confused. Also signal health is not a good name if we integrate things like bandwidth congestion.
• Can integrate Bandwidth congestion and rate from radio driver #479 into the same signal health format.

[gemenerik]

The C++ link driver's 'link quality' implementation is different from the (default) radio driver's. The the C++ link driver's implementation is based on the percentage of messages acked, while the radio driver's implementation is based on the number of retries. The structure introduced in this PR is a work in progress, but given that they hook into the same callback, I may want to unify them.

[gemenerik]

4435c7c and 73963e0 combine #479 into this, updating PR to reflect

[gemenerik]

Also, I verified, and the way this is set up currently, it does not break compatibility with cfclient