Implement betaflight-style VTX control over MSP so an MSP VTX (or an OSD
acting as one) can be configured from ArduPilot:
- reply to MSP_VTX_CONFIG and push config as MSP v2 native
- apply frequency changes from MSP_SET_VTX_CONFIG
- learn the power table from MSP_SET_VTXTABLE_POWERLEVEL and decode it
as dBm
- report the configured pitmode in MSP_VTX_CONFIG
- report the FC variant matching the active OSD symbol set
- option to hold the VTX at high power while disarmed
Process outgoing packets so config can be pushed unsolicited, and guard
the DisplayPort scheduler when VideoTX is disabled. The whole path is
gated on AP_MSP_VIDEOTX_ENABLED.