Per-thread logging flag must be made immutable
Description of problem:
The problem is that the code assumes it isn't possible to switch from global logging to per-thread logging and vice-versa per design, but it lags appropriate checks to enforce it. Enabling or disabling per-thread logging at runtime from the monitor causes unexpected results.
Steps to reproduce:
Enabling per-thread logging at runtime:

1. Start QEMU : `./qemu-system-x86_64 -S -monitor stdio -D qemu.log.%d`
2. Enable per-thread logging from the HMP monitor : `(qemu) log tid`
3. Fails with `Filename template with '%d' required for 'tid'` even though such a template was passed with `-D`.

Disabling per-thread logging at runtime:

1. Start QEMU : `./qemu-system-x86_64 -S -monitor stdio -D qemu.log.%d -d tid,cpu_reset`
2. Disable per-thread logging from the HMP monitor: `(qemu) log cpu_reset`
3. QEMU creates a log file with a bogus `qemu.log.%d` name.
Additional information:
[Series](https://patchew.org/QEMU/20221104120059.678470-1-groug@kaod.org/) posted and already reviewed by @rth7680 .