Kconfig: BT: Give the LL selection option a name
Kconfig: BT: Give the LL selection option a name

There is an unnamed choice for the BT link layer selection.

Giving the choice a name would allow multiple declarations of the
option and the ability to select out-of-tree LL's.

Signed-off-by: Sebastian Bøe <edee888afd63e94916688495334700803eba20a0@nordicsemi.no>

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