MinimOSD Enable Telemetry button should only update the required SR0_ or SR3_ params

Pushing this button currently updates both the SR0_ and SR3_ parameters but this essentially causes the APM to send telemetry updates to two uarts when only 1 will be required. ArduCopter in particular is quite low on CPU and we need to reduce unnecessary work as much as possible. thanks!

Locate the MinimOSD Enable Telemetry button and the code that updates SR0_ and SR3_ parameters. Trace how the required telemetry UART is selected, then verify that enabling telemetry updates only that parameter group rather than both.

Written by the indexing model from the issue text.