* fix(mavlink): align signing with MAVLink spec and fix performance regression
Remove the non-standard MAV_SIGN_CFG parameter and align the signing
implementation with the MAVLink specification.
Key changes:
- Remove MAV_SIGN_CFG parameter that conflicted with GCS implementations
- Only enable signing when a valid key is present on the SD card
- Accept SETUP_SIGNING on any link, not just USB
- Reject SETUP_SIGNING while the vehicle is armed
- Allow disabling signing via signed all-zero key SETUP_SIGNING message
- Propagate key changes to all mavlink instances
- Zero CPU/bandwidth overhead when signing is not active
Fixes#26893
Signed-off-by: Ramon Roche <mrpollo@gmail.com>
* Signing minor subedit
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Signed-off-by: Ramon Roche <mrpollo@gmail.com>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>
Co-authored-by: Jacob Dahl <dahl.jakejacob@gmail.com>
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