test: add btusb ZLP quirk for issue 63

tests/issue63-btusb-zlp/README.md

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+# Issue #63: system `btusb` ZLP test
+
+This test keeps the normal `aic_load_fw + btusb` architecture. It does not
+restore or install the vendor `aic_btusb` driver.
+
+The patch adds one quirk to the standard Linux `btusb` source:
+
+- match only AICSemi `368b:8d81`;
+- set `URB_ZERO_PACKET` on Bluetooth ACL bulk OUT transfers;
+- leave every other `btusb` device and code path unchanged.
+
+The test installer downloads the standard `btusb` source matching the running
+kernel's upstream version, applies the patch, and installs the resulting
+`btusb.ko` through DKMS. The distribution module is not overwritten and can be
+restored by removing the DKMS test package.
+
+## Install the test module
+
+On Fedora, make sure the test build dependencies are installed:
+
+```bash
+sudo dnf install dkms gcc make kernel-devel-$(uname -r) curl patch
+```
+
+Stop Bluetooth scanning and disconnect Bluetooth devices, then run:
+
+```bash
+cd tests/issue63-btusb-zlp
+sudo ./btusb-zlp-test.sh install
+./btusb-zlp-test.sh status
+```
+
+`modinfo -n btusb` should point to an `updates/dkms` path. Secure Boot systems
+may require the DKMS module to be signed or enrolled before it can load.
+
+Select AAC again and play audio for at least one hour:
+
+```bash
+bluetoothctl scan off
+pactl set-card-profile bluez_card.28_6F_40_46_AB_B1 a2dp-sink-aac
+```
+
+Please capture `sudo btmon -w issue63-zlp.btsnoop` and relevant `dmesg` lines if
+the connection still stalls.
+
+## Restore the distribution module
+
+```bash
+sudo ./btusb-zlp-test.sh remove
+./btusb-zlp-test.sh status
+```
+
+After removal, `modinfo -n btusb` should point back to the distribution's
+`kernel/drivers/bluetooth/btusb.ko` path.
+
+## Scope
+
+This is an A/B diagnostic patch, not a production workaround. If AAC remains
+stable, the small kernel patch can be submitted upstream. If it still fails,
+the next isolated experiment should add an AIC-specific runtime-PM quirk rather
+than replacing the standard Bluetooth driver.