Bluetooth: Mesh: Fixes Config client send publish message
Bluetooth: Mesh: Fixes Config client send publish message

When Config client model send publish message, app_idx will
be need, however, currently code clear this value use `&`,
this will be generate error when app_idx not zero.

Signed-off-by: Lingao Meng <8f6064192f8620c0146f45d3572dde5f622ecf12@gmail.com>

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