Fix: Add ifindex field for Linux

- Move ifindex field outside WIN32 conditional block
- Initialize ifindex in Linux tun_platform_init()

src/tun_if.h

@@ -50,13 +50,14 @@ struct tun_if {
     uint32_t packets_written;
     uint32_t read_errors;
     uint32_t write_errors;
+    
+    uint32_t ifindex;              // интерфейсный индекс
 
 #ifdef _WIN32
     CRITICAL_SECTION output_queue_lock;   // защита output_queue (TUN → routing)
     HANDLE           read_thread;
     HANDLE           stop_event;
     volatile int     running;             // 1 = поток работает
-    DWORD            ifindex;              // Windows: интерфейсный индекс
 #endif
 };
 

src/tun_linux.c

@@ -195,6 +195,11 @@ int tun_platform_init(struct tun_if* tun, const char* ifname, const char* ip_str
         tun->fd = -1;
         return -1;
     }
+    
+    tun->ifindex = if_nametoindex(tun->ifname);
+    if (tun->ifindex == 0) {
+        DEBUG_ERROR(DEBUG_CATEGORY_TUN, "Failed to get ifindex for %s", tun->ifname);
+    }
 
     // Set non-blocking mode
     int flags = fcntl(tun->fd, F_GETFL, 0);