Reverts #3952

…#3988)

## What does this implement/fix?

When a player's DSP settings are changed while the main DSP toggle is
**disabled**, the active playback was unnecessarily restarted, causing
audio stutter and a misleading `Restarting playback of Player <id> after
DSP change` log line.

The fix reads the old `enabled` state in `save_dsp_config` before saving
the new config. `on_player_dsp_change` is only called when DSP was or is
now enabled — covering all cases that actually affect the active audio
stream (e.g. toggling DSP off still triggers a restart to flush the old
processing chain). If DSP was already disabled and stays disabled, the
call is skipped entirely.

**Related issue (if applicable):**

- related issue music-assistant/support#5532

## Types of changes

- [x] Bugfix (non-breaking change which fixes an issue) — `bugfix`
- [ ] New feature (non-breaking change which adds functionality) —
`new-feature`
- [ ] Enhancement to an existing feature — `enhancement`
- [ ] New music/player/metadata/plugin provider — `new-provider`
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected) — `breaking-change`
- [ ] Refactor (no behaviour change) — `refactor`
- [ ] Documentation only — `documentation`
- [ ] Maintenance / chore — `maintenance`
- [ ] CI / workflow change — `ci`
- [ ] Dependencies bump — `dependencies`

## Checklist

- [ ] The code change is tested and works locally.
- [x] `pre-commit run --all-files` passes.
- [x] `pytest` passes, and tests have been added/updated under `tests/`
where applicable.
- [ ] For changes to shared models, the companion PR in
`music-assistant/models` is linked.
- [ ] For changes affecting the UI, the companion PR in
`music-assistant/frontend` is linked.
- [x] I have read and complied with the project's [AI
Policy](https://github.com/music-assistant/.github/blob/main/AI_POLICY.md)
for any AI-assisted contributions.

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Co-authored-by: Claude <noreply@anthropic.com>