boards: 96boards: carbon: Increase main stack size when using Bluetooth

Increase main stack size when MBEDTLS_INIT is enabled to avoid stack
overflow as it consumes 1536 bytes.

Signed-off-by: Ali Hozhabri <ali.hozhabri@st.com>

Author: HoZHel

boards/96boards/carbon/Kconfig.defconfig

@@ -9,6 +9,9 @@ config SPI_STM32_INTERRUPT
 	default y
 	depends on SPI
 
+configdefault MAIN_STACK_SIZE
+	default 1600 if MBEDTLS_INIT
+
 endif # BOARD_96B_CARBON_STM32F401XE
 
 if BOARD_96B_CARBON_NRF51822