bluetooth: controller: Refactor PDU_RX_POOL_SIZE
bluetooth: controller: Refactor PDU_RX_POOL_SIZE

Refactor PDU_RX_POOL_SIZE into its constituents and name each term.

No functional change expected.

Signed-off-by: Mark Ruvald Pedersen <3c05dc905675c0722f67ee578faf639727313efa@oticon.com>

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