Bluetooth: hci-uart: Use a fiber to offload TX from ISR
Bluetooth: hci-uart: Use a fiber to offload TX from ISR

Due to the fact that ISRs run at priority 1, the LE_Rand
command was not being rescheduled after CPU sleep to be
able to fill its buffers. By performing all TX (to controller)
work on a fiber, the RNG ISR is able to run and the command
can be executed synchronously in the fiber context.

Change-Id: I3b658e1cab3f80ae655cc88566639a122a361a08
Signed-off-by: Carles Cufi <853081dc8dca4fe6a7e3c984752718b5db36e060@nordicsemi.no>

GiulianoFranchetto/zephyr,tidyjiang8/zephyr-doc,Vudentz/zephyr,fractalclone/zephyr-riscv,holtmann/zephyr,mbolivar/zephyr,rsalveti/zephyr,fbsder/zephyr,sharronliu/zephyr,zephyriot/zephyr,punitvara/zephyr,bigdinotech/zephyr,pklazy/zephyr,runchip/zephyr-cc3200,galak/zephyr,rsalveti/zephyr,explora26/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,tidyjiang8/zephyr-doc,fbsder/zephyr,finikorg/zephyr,zephyriot/zephyr,fbsder/zephyr,nashif/zephyr,galak/zephyr,kraj/zephyr,erwango/zephyr,ldts/zephyr,bboozzoo/zephyr,runchip/zephyr-cc3200,bboozzoo/zephyr,punitvara/zephyr,nashif/zephyr,kraj/zephyr,erwango/zephyr,kraj/zephyr,runchip/zephyr-cc3220,Vudentz/zephyr,runchip/zephyr-cc3220,ldts/zephyr,holtmann/zephyr,runchip/zephyr-cc3220,explora26/zephyr,sharronliu/zephyr,finikorg/zephyr,ldts/zephyr,explora26/zephyr,mbolivar/zephyr,erwango/zephyr,tidyjiang8/zephyr-doc,finikorg/zephyr,holtmann/zephyr,aceofall/zephyr-iotos,punitvara/zephyr,erwango/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,punitvara/zephyr,pklazy/zephyr,GiulianoFranchetto/zephyr,fractalclone/zephyr-riscv,runchip/zephyr-cc3200,explora26/zephyr,zephyriot/zephyr,pklazy/zephyr,sharronliu/zephyr,GiulianoFranchetto/zephyr,bigdinotech/zephyr,tidyjiang8/zephyr-doc,rsalveti/zephyr,bboozzoo/zephyr,finikorg/zephyr,kraj/zephyr,sharronliu/zephyr,fbsder/zephyr,pklazy/zephyr,ldts/zephyr,aceofall/zephyr-iotos,holtmann/zephyr,galak/zephyr,aceofall/zephyr-iotos,ldts/zephyr,nashif/zephyr,mbolivar/zephyr,Vudentz/zephyr,fbsder/zephyr,zephyriot/zephyr,bboozzoo/zephyr,runchip/zephyr-cc3220,Vudentz/zephyr,bigdinotech/zephyr,mbolivar/zephyr,zephyrproject-rtos/zephyr,bigdinotech/zephyr,aceofall/zephyr-iotos,fractalclone/zephyr-riscv,kraj/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,aceofall/zephyr-iotos,pklazy/zephyr,runchip/zephyr-cc3200,holtmann/zephyr,punitvara/zephyr,rsalveti/zephyr,tidyjiang8/zephyr-doc,Vudentz/zephyr,zephyrproject-rtos/zephyr,runchip/zephyr-cc3200,fractalclone/zephyr-riscv,fractalclone/zephyr-riscv,explora26/zephyr,bigdinotech/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,bboozzoo/zephyr,zephyriot/zephyr,sharronliu/zephyr,galak/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,rsalveti/zephyr,erwango/zephyr