Fix strange RTL behavior

This commits have fixed #1441 for me. Please review and cross test.

The behaviour should now be:

For COM_DL_LOSS_EN ==0:

- Mission finished, no RC, datalink ok: AUTO_RCRECOVER (RTL)
- Mission finished, no RC, datalink lost: AUTO_RCRECOVER (RTL)

For COM_DL_LOSS_EN == 1:

- Mission finished, no RC, datalink ok: AUTO_MISSION (loitering)
- Mission finished, no RC, datalink lost: AUTO_RCRECOVER (RTL)