h-flow: enable CAN termination in software

[julianoes]

This enables setting the CAN termination by setting a parameter.

Needs testing by @vincentpoont2.

[github-actions]

FLASH Analysis

px4_fmu-v5x

    FILE SIZE        VM SIZE    
--------------  -------------- 
+0.0%      +8  +0.0%      +8    .text
-0.1%      -8  [ = ]       0    [Unmapped]
[ = ]       0  +0.0%      +8    TOTAL

px4_fmu-v6x

    FILE SIZE        VM SIZE    
--------------  -------------- 
[ = ]       0  [ = ]       0    TOTAL

Updated: 2024-12-03T23:59:06

[hamishwillee]

Also docs, since those don't say very much about CAN termination - https://docs.px4.io/main/en/can/#wiring - essentially that you need a resistor or similar. We could say more.

[julianoes]

Closing in favor of #24086.