Bluetooth: tester: Fix using invalid elements with k_fifo
Bluetooth: tester: Fix using invalid elements with k_fifo

The documentation of k_fifo_put mentions that the items must have 32
bits reserved for kernel use as that is where the sys_snode_t pointer
is placed but this detail was not taken into consideration when
designing the cmd_queue which access each element as a btp_cmd.

Note: This probably used to work just because k_fifo_get used to place
data directly into thread's swap_data so the kernel never really touched
the list but with the changes to use k_poll the list is always updated
exposing this issue.

Jira: ZEP-2568

Signed-off-by: Luiz Augusto von Dentz <8530c5ea66a1bdbc08f98bfcf183c8be901b5990@intel.com>

punitvara/zephyr,zephyriot/zephyr,explora26/zephyr,punitvara/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr,aceofall/zephyr-iotos,mbolivar/zephyr,ldts/zephyr,nashif/zephyr,kraj/zephyr,galak/zephyr,explora26/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,galak/zephyr,fbsder/zephyr,zephyriot/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,nashif/zephyr,galak/zephyr,fbsder/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,galak/zephyr,fbsder/zephyr,aceofall/zephyr-iotos,GiulianoFranchetto/zephyr,mbolivar/zephyr,zephyriot/zephyr,galak/zephyr,runchip/zephyr-cc3220,mbolivar/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,explora26/zephyr,runchip/zephyr-cc3220,aceofall/zephyr-iotos,aceofall/zephyr-iotos,kraj/zephyr,Vudentz/zephyr,fbsder/zephyr,Vudentz/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,kraj/zephyr,kraj/zephyr,aceofall/zephyr-iotos,GiulianoFranchetto/zephyr,finikorg/zephyr,ldts/zephyr,punitvara/zephyr,finikorg/zephyr,punitvara/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,zephyriot/zephyr,nashif/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,ldts/zephyr,nashif/zephyr,fbsder/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr