Bluetooth: Controller: Fine-tune stack sizes for nRF51

The actual usage is substantially less than the default when using minimal
configurations on nRF51:

 BT CTLR RX          : STACK: unused 32 usage 288 / 320 (90 %); CPU: 0 %
 BT CTLR RX pri      : STACK: unused 32 usage 344 / 376 (91 %); CPU: 0 %

Signed-off-by: Johan Hedberg <[email protected]>

Author: jhedberg

subsys/bluetooth/controller/Kconfig.ll_sw_split

@@ -127,6 +127,7 @@ config BT_CTLR_RX_PRIO_STACK_SIZE
 	# Hidden
 	int
 	depends on !BT_HCI_RAW
+	default 376 if SOC_SERIES_NRF51X && !BT_EXT_ADV
 	default 448
 	help
 	  Controller's Co-Operative high priority Rx thread stack size.
@@ -141,6 +142,7 @@ config BT_CTLR_RX_PRIO_STACK_SIZE
 config BT_CTLR_RX_STACK_SIZE
 	# Hidden, Controller's Co-Operative Rx thread stack size.
 	int
+	default 320 if SOC_SERIES_NRF51X && !BT_EXT_ADV
 	default 896
 
 config BT_CTLR_SETTINGS