fix(qemu_mps2_an385): increase stack size from 8KB to 24KB to prevent boot-time stack overflow

After commit f6e8d61, NetIface::new() is called during net::init() which
runs on the interrupt stack (CONFIG_STACK_SIZE=8KB). smoltcp::Interface::new()
internally performs a ~14KB memset in Fragmenter::new(), overflowing the 8KB
stack and corrupting the TLSF allocator's sentinel block.

Increase CONFIG_STACK_SIZE to 24KB across all three defconfig variants, and
bump the heap alignment in link.x from 8 to 16 bytes for correctness.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: xuchang-vivo

arch/arm/cortex_m/link.x

@@ -209,7 +209,7 @@ SECTIONS
 
   .heap (COPY) :
   {
-    . = ALIGN(8);
+    . = ALIGN(16);
     PROVIDE(_end = .);
     __heap_start = .;
     . = ORIGIN(RAM) + LENGTH(RAM) - STACK_SIZE - STACK_GUARD_SIZE;

kconfig/config/qemu_mps2_an385/coverage/defconfig

@@ -74,6 +74,6 @@ CONFIG_CMSIS_RTOS2_ADAPTER=y
 # linker script
 CONFIG_SRAM_BASE_ADDRESS=0x21000000
 CONFIG_SRAM_SIZE=16384
-CONFIG_STACK_SIZE=8
+CONFIG_STACK_SIZE=24
 CONFIG_FLASH_BASE_ADDRESS=0x0
 CONFIG_FLASH_SIZE=4096

kconfig/config/qemu_mps2_an385/debug/defconfig

@@ -74,6 +74,6 @@ CONFIG_CMSIS_RTOS2_ADAPTER=y
 # linker script
 CONFIG_SRAM_BASE_ADDRESS=0x21000000
 CONFIG_SRAM_SIZE=16384
-CONFIG_STACK_SIZE=8
+CONFIG_STACK_SIZE=24
 CONFIG_FLASH_BASE_ADDRESS=0x0
 CONFIG_FLASH_SIZE=4096

kconfig/config/qemu_mps2_an385/release/defconfig

@@ -74,6 +74,6 @@ CONFIG_CMSIS_RTOS2_ADAPTER=y
 # linker script
 CONFIG_SRAM_BASE_ADDRESS=0x21000000
 CONFIG_SRAM_SIZE=16384
-CONFIG_STACK_SIZE=8
+CONFIG_STACK_SIZE=24
 CONFIG_FLASH_BASE_ADDRESS=0x0
 CONFIG_FLASH_SIZE=4096