Resolved connection leak in SNI by adding dispose for underlying TCP …

…stream in SNITcpHandle.Dispose()

src/System.Data.SqlClient/src/System/Data/SqlClient/SNI/SNITcpHandle.cs

@@ -22,7 +22,7 @@ internal class SNITCPHandle : SNIHandle
         private readonly string _targetServer;
         private readonly object _callbackObject;
         private readonly Socket _socket;
-        private readonly NetworkStream _tcpStream;
+        private NetworkStream _tcpStream;
         private readonly TaskScheduler _writeScheduler;
         private readonly TaskFactory _writeTaskFactory;
 
@@ -57,6 +57,12 @@ public override void Dispose()
                     _sslStream.Dispose();
                     _sslStream = null;
                 }
+
+                if (_tcpStream != null)
+                {
+                    _tcpStream.Dispose();
+                    _tcpStream = null;
+                }
             }
         }