Socks inbound: Fix stats for UDP Associate traffic (#7101)

https://github.com/XTLS/Xray-core/pull/7101#pullrequestreview-5452526703

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Co-authored-by: 风扇滑翔翼 <Fangliding.fshxy@outlook.com>

proxy/socks/server.go

@@ -170,9 +170,17 @@ func (s *Server) processTCP(ctx context.Context, conn stat.Connection, dispatche
 			return errors.New("UDP associate with listen port failed")
 		}
 		tempUDPConn.SetTimeout(plcy.Timeouts.ConnectionIdle)
+		var udpConn stat.Connection = tempUDPConn
+		if counters, ok := conn.(*stat.CounterConnection); ok {
+			udpConn = &stat.CounterConnection{
+				Connection:   tempUDPConn,
+				ReadCounter:  counters.ReadCounter,
+				WriteCounter: counters.WriteCounter,
+			}
+		}
 		errCh := make(chan error, 1)
 		go func() {
-			errCh <- s.handleUDPPayload(ctx, tempUDPConn, dispatcher)
+			errCh <- s.handleUDPPayload(ctx, udpConn, dispatcher)
 		}()
 		// Associated TCP keeps the UDP alive
 		// Close UDP if TCP connection is closed