4.3.0-RC7 with AKK / RDQ smartaudio fix

Continuation of the older 4.2 branch https://github.com/betaflight/betaflight/tree/akk_vtx_fix but ported to 4.3.0-RC7

Fix adds trailing bytes to the smartaudio data to be compatible with early AKK / RDQ smartaudio VTXs.

Betaflight 4.3.0 is unreleased software and has not been fully tested. Please take care when testing this.

Betaflight Configurator RC7 release or newer is required to configure Betaflight 4.3 RC7: https://github.com/betaflight/betaflight-configurator/releases/tag/10.8.0-RC7

Installation:

1. Backup a diff of your config in betaflight, in CLI do diff all
   • the paranoid among you may wish to do a dump if you are running a non-official firmware e.g. a vendor-built firmware.
2. Download firmware below matching your flight controller MCU model.
3. Open Configurator 10.8.0+ and select your FC model
4. Flash the firmware - in Betaflight Configurator Firmware Updater choose "local file"
5. If your diff is from 4.3 put it all in, otherwise you can put in most things except the PID and filter sections.
   • some config items have changed names during 4.3 development including slider names, if your 4.3 config is older you may need to reset the some sliders to defaults