Bluetooth: shell: adding command for directed advertising
Bluetooth: shell: adding command for directed advertising

Added a new command, which can be used to test the directed advertising
API. This command allows user to turn on directed advertising in two
modes: low and high duty. High duty mode is the default one.

Signed-off-by: Kamil Piszczek <94a00d4c21e2b5f86e16c4df4b1ac94e543626d8@nordicsemi.no>

kraj/zephyr,explora26/zephyr,ldts/zephyr,Vudentz/zephyr,explora26/zephyr,Vudentz/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,punitvara/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,finikorg/zephyr,nashif/zephyr,nashif/zephyr,explora26/zephyr,galak/zephyr,ldts/zephyr,ldts/zephyr,finikorg/zephyr,finikorg/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,kraj/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,kraj/zephyr,punitvara/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,nashif/zephyr,ldts/zephyr,finikorg/zephyr