Return payload even if NOK is set in the frame header.

[dehanj]

Description

The idea is to return the payload to the client application, even if the NOK bit is set in the framing header. This would allow for the application to utilize this for more expressive error handling if they want to. In short, give more freedom to the application developer, but still within the realm of the framing protocol.

Fixes #10

Type of change

• Feature (non breaking change which adds functionality)

Submission checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my changes
• I have tested and verified my changes on target
• My changes are well written and CI is passing
• I have squashed my work to relevant commits and rebased on main for linear history
• I have added a "Co-authored-by: x" if several people contributed, either pair programming or by squashing commits from different authors.
• I have updated the documentation where relevant (readme, dev.tillitis.se etc.)
• QEMU is updated to reflect changes