- moved methods used to modify channel maximum pwm value to VtolType
class so that the can be shared by the differnt vtol types

Signed-off-by: Roman <bapstroman@gmail.com>

 - closes #9277

- disables setting of the errno variable as required by C89/C99 on calling math library routines

- Addional small cleanup of the iridium driver and the include guards of mavlink module header files

Due to the old heartbeat of the high latency telemetry when activating it after flying sufficiently long in normal telemetry it is first detected as lost until the first message is sent.
By updating the heartbeat to the current time on switching this issue is avoided.

Also includes a small style fix for the HIGH_LATENCY2 stream

- Check if changing to a non standby state if the current state is the standy state and no change is already scheduled.
- Add prefix _ to all class variables

- Allow using the full buffer size (340 bytes)
- Add tx mutex for sbd session to avoid dropping message which are written during an sbd session

- Every time data is written to the iridium module all previous untransmitted data is overwritten
- The buffer is reset only on the following conditions
    - A sbd session is successfully completed
    - An incoming mavlink message would result in less than SATCOM_MIN_TX_BUF_SPACE free bytes after it is written
    - Any other incomming data would result in less than SATCOM_MIN_TX_BUF_SPACE free bytes after it is written to the buffer.