Bluetooth: shell: Fix null check in conn and data length update
Bluetooth: shell: Fix null check in conn and data length update

Perform null check of default_conn in call cmd_conn_update()
and cmd_conn_data_len_update() in ./subsys/bluetooth/shell/bt.c

Signed-off-by: Kai Ren <3f6ec023d7257eefda1449bca95ed6a4ef197796@163.com>

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