when executing 'logger stop' and the logger did not log yet, _running was
false, so log_writer thread would never exit.

Since it's only used in run().

This also greatly speeds up the generators.

This makes sure the file descriptors are closed in the right thread.
Before on NuttX, when stopping the logger, orb unsubscribe failed due to
this.

We always write larger chunks (orb messages) to the buffer, so the buffer
needs to be larger than the minimum write chunk

write_changed_parameters() also takes the lock and thus would deadlock
otherwise.

This is required for the logger, we just manually add the padding bytes
what would otherwise be done by the compiler. Additionally we reorder
the fields by type, so that padding is only necessary for nested types.