testing/ltp: Increase Stack Size

Inside CI Build risc-v-05: `rv-virt:citest` fails with a Stack Overflow at ltp_interfaces_pthread_barrierattr_init_2_1:
- apache/nuttx#15170

This PR doubles the Stack Size for `testing/ltp` (from 4096 bytes to 8192), so that `rv-virt:citest` completes successfully.

Author: lupyuen

testing/ltp/Kconfig

@@ -13,6 +13,6 @@ if TESTING_LTP
 
 config TESTING_LTP_STACKSIZE
 	int "Linux Test Project stack size"
-	default 4096
+	default 8192
 
 endif #TESTING_LTP