tests: bluetooth: tester: Fix not marking chan as unused on disconnect
tests: bluetooth: tester: Fix not marking chan as unused on disconnect

This fix not being able to re-connect channel after disconnect.

Signed-off-by: Szymon Janc <db186c297188f7acbbdc9bbd6aff2f45665bb42d@codecoup.pl>

finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,galak/zephyr