Bluetooth: conn: Fix invalid state transition
Bluetooth: conn: Fix invalid state transition

When initiating a disconnection conn_disconnect would be called to send
HCI_Disconnect but the controller may be quick enough to send Disconnect
Complete event before setting BT_CONN_DISCONNECT which will then cause
the invalid transition from BT_CONN_DISCONNECTED to BT_CONN_DISCONNECT
and the connection won't be freed properly.

Signed-off-by: Luiz Augusto von Dentz <8530c5ea66a1bdbc08f98bfcf183c8be901b5990@intel.com>

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