add multiplexer/router

in case a remote is disconnected and can be reconnected quickly,
a seamless routing is possible. However, when after reconnection
the description has changed, the server is restarted.

+ more information in error messages from dispatcher

Change-Id: I0837e0254aee3d12a26481f6fd697081a53aabba
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/22506
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>

secop/protocol/interface/tcp.py

@@ -221,6 +221,7 @@ class TCPServer(HasProperties, socketserver.ThreadingTCPServer):
         self.setProperty('detailed_errors', detailed_errors)
         self.checkProperties()
 
+        self.allow_reuse_address = True
         self.log.info("TCPServer %s binding to %s:%d" % (name, self.bindto, self.bindport))
         socketserver.ThreadingTCPServer.__init__(
             self, (self.bindto, self.bindport), TCPRequestHandler, bind_and_activate=True)