Fix remaining Windows test build issues

- Remove sys/socket.h include from test_etcp_two_instances.c (Linux-only)
- Fix test_mkdtemp buffer overflow - use memcpy instead of strncpy
- Fix test_mkdtemp return value check (replace == NULL with != 0)
- Add Windows socket libraries (-lws2_32 -liphlpapi) to test builds
- All tests build successfully on Linux

tests/Makefile.am

@@ -76,7 +76,14 @@ ETCP_FULL_OBJS = \
 	$(ETCP_CORE_OBJS)
 
 # Common libraries (libuasync.a from lib directory)
-COMMON_LIBS = $(top_builddir)/lib/libuasync.a -lpthread
+COMMON_LIBS = $(top_builddir)/lib/libuasync.a -lpthread $(WIN_LIBS)
+
+# Windows-specific libraries
+if OS_WINDOWS
+WIN_LIBS = -lws2_32 -liphlpapi
+else
+WIN_LIBS =
+endif
 
 # Crypto libraries (conditional)
 if USE_OPENSSL

tests/test_etcp_two_instances.c

@@ -11,7 +11,6 @@
 #endif
 #include <time.h>
 #include <sys/stat.h>
-#include <sys/socket.h>
 
 #include "../src/etcp.h"
 #include "../src/etcp_connections.h"
@@ -71,7 +70,7 @@ static const char* client_config_content =
 
 // Create temp config files
 static int create_temp_configs(void) {
-    if (test_mkdtemp(temp_dir) == NULL) {
+    if (test_mkdtemp(temp_dir) != 0) {
         fprintf(stderr, "Failed to create temp directory\n");
         return -1;
     }

tests/test_utils.h

@@ -20,7 +20,6 @@ static char test_temp_dir[MAX_PATH];
 
 // Cross-platform mkdtemp for Windows
 static inline int test_mkdtemp(char *template_str) {
-    (void)template_str;  // Not used on Windows, we generate our own path
     char tmp_path[MAX_PATH];
     GetTempPathA(MAX_PATH, tmp_path);
     
@@ -31,9 +30,10 @@ static inline int test_mkdtemp(char *template_str) {
         snprintf(test_temp_dir, sizeof(test_temp_dir), "%s\\utun_test_%08x", 
                  tmp_path, (unsigned int)rand());
         if (_mkdir(test_temp_dir) == 0) {
-            // Copy path back to caller's buffer
+            // Copy path back to caller's buffer if provided
             if (template_str) {
-                strncpy(template_str, test_temp_dir, MAX_PATH);
+                size_t len = strlen(test_temp_dir);
+                memcpy(template_str, test_temp_dir, len + 1);  // Include null terminator
             }
             return 0;  // Success
         }