Reduce thread stack size for parallel network tests

This commit reduces the thread stack from 2k to 1k for each thread in
the parallel network tests. This allows the test to run on more
constrained devices (like the LPC1768).

features/FEATURE_LWIP/TESTS/mbedmicro-net/tcp_echo_parallel/main.cpp

@@ -42,6 +42,10 @@ private:
     Thread thread;
 
 public:
+    // Limiting stack size to 1k
+    Echo(): thread(osPriorityNormal, 1024) {
+    }
+
     void start() {
         osStatus status = thread.start(callback(this, &Echo::echo));
         TEST_ASSERT_EQUAL(osOK, status);

features/FEATURE_LWIP/TESTS/mbedmicro-net/udp_echo_parallel/main.cpp

@@ -46,6 +46,10 @@ private:
     Thread thread;
 
 public:
+    // Limiting stack size to 1k
+    Echo(): thread(osPriorityNormal, 1024) {
+    }
+
     void start() {
         osStatus status = thread.start(callback(this, &Echo::echo));
         TEST_ASSERT_EQUAL(osOK, status);