Bluetooth: host: Allow only one legacy advertising instance
Bluetooth: host: Allow only one legacy advertising instance

When legacy advertising enable command is issues,
the BT_ADV_ADVERTISING has to be set, because this
flag is checked in many scenarios to see if the
advertising is ongoing or not.

Signed-off-by: Ahmed Shokry <b13dfcae54898af1345b823d6015c9f506c7e4e8@synopsys.com>

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