[Bugfix] Logging broadcast

[elpekenin]

Description

I was developing a custom sendchar on my fork, sending XAP messages too, and the client kept crashing upon receiving those...

Ended up noticing a mismatch between fw's implementation and specification of the xap.Broadcast.Logging (which was the thing that lead me into sending a wrong payload)

There have been a couple of commits after that, which indicate that the header(and not first byte of payload) will actually be in charge of the task:

• https://github.com/qmk/qmk_firmware/commit/980699f3cfd4761c9a2acdbb39d8283a6518694e
• https://github.com/qmk/qmk_firmware/commit/87fd4b42f5bccc6c53b4183bb4740c9e5ae8ed3d

Thus, this is now the correct way of handling it...

Should perhaps wait a bit before merging, just to make 100% sure this will be the final way of doing it.