support ohos (#974)

* support ohos

---------

Co-authored-by: FrankHan <2777926911@qq.com>

easytier-contrib/easytier-ffi/src/lib.rs

@@ -29,6 +29,30 @@ fn set_error_msg(msg: &str) {
     msg_buf[..len].copy_from_slice(bytes);
 }
 
+#[no_mangle]
+pub extern "C" fn set_tun_fd(
+    inst_name: *const std::ffi::c_char,
+    fd: std::ffi::c_int,
+) -> std::ffi::c_int {
+    let inst_name = unsafe {
+        assert!(!inst_name.is_null());
+        std::ffi::CStr::from_ptr(inst_name)
+            .to_string_lossy()
+            .into_owned()
+    };
+    if !INSTANCE_NAME_ID_MAP.contains_key(&inst_name) {
+        return -1;
+    }
+    match INSTANCE_MANAGER.set_tun_fd(&INSTANCE_NAME_ID_MAP.get(&inst_name).unwrap().value(), fd) {
+        Ok(_) => {
+            0
+        }
+        Err(_) => {
+            -1
+        }
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn get_error_msg(out: *mut *const std::ffi::c_char) {
     let msg_buf = ERROR_MSG.lock().unwrap();