[Bug] Mode switch from hold mode to an unassigned mode triggers mode change

[Jaeyoung-Lim]

Describe the bug

We had a crash when doing autonomous missions while in HOLD mode.

What happened was that the RC seemed to had a slight glitch, where the value of the mode switch changed.

This made the mode switch to briefly be at the unassigned mode value, which raised the switch_changes in the manual_control_switch message. As you can see in the image below, mode_slot 3, 4, 5 was assigned as Manual, Altitude, Position but the position switch breifly goes to mode_slot 2

This triggered a mode switch from HOLD mode to Manual, where the throttle stick was at zero, resulting in a crash.

The main issue is that mode_slot 2, which triggered the mode change, is a position not achievable with the three position switch on my Taranis 9X. Moreover, it was an unassigned mode_slot which triggered the change.

To Reproduce

1. Configure the RC mode switch to an unassigned mode slot
2. Put the vehicle in hold mode
3. Transition to an unassigned mode

Expected behavior

If the mode_slot is unassigned, the vehicle should stay in HOLD mode.

Screenshot / Media

Flight Log

https://review.px4.io/plot_app?log=8867de8d-b255-4d66-ab0a-b7e8029c4876

Software Version

9887058 (with added DDS topics: ethz-asl@bb7c6f4)

Flight controller

Pixhawk 4

Vehicle type

Multicopter

How are the different components wired up (including port information)

No response

Additional context

No response