No remote request flag is set when sending such frame with interface socketcand

### Describe the bug
When sending a frame like
```python
bus = can.interface.Bus(interface='socketcand', channel='can0', host='the.ipa.ddr.ess', port=29536)
...
can_msg = can.Message(is_extended_id = False, arbitration_id = address, is_remote_frame = True)
self.bus.send(can_msg)
```
the terminal message print is:
```
Timestamp: 0.000000 ID: 403 S Rx R DL: 0
```
but on the bus be get (using candump):
```
can0 403 [0] ''
```
kinda empty frames.

When using the direct can0 interface (no socketcand) I get correctly:
```
can0 403 [0] remote request
```

### To Reproduce
Using python_can==4.6.1 on a Mac with Python 3.9.6.
socketcand Version 0.6.1 is running on a Debian 13.

### Expected behavior
Seeing correct remote request frames

從 can.interface.Bus 開始，設定 interface='socketcand'，並在 can.Message 將 is_remote_frame=True 時追蹤 self.bus.send(can_msg)。將 socketcand 路徑與直接的 can0 路徑進行比較，並使用 candump 驗證結果。完成的條件是，傳輸的訊框被回報為遠端請求，而不是空資料訊框。

由索引模型根據 Issue 內容生成。