fix broken links in telnetsrv.md

common/utils/telnetsrv/DOC/telnetsrv.md

 The oai embedded telnet server is an optional monitoring and debugging tool. It provides a simple Command Line Interface to the oai softmem. New commands can easily be added by developers to the telnet server.
 
-* [Using the telnet server](telnetusage)
-* [Adding commands to the oai telnet server](telnetaddcmd)
-* [telnet server architecture ](telnetarch)
+* [Using the telnet server](telnetusage.md)
+* [Adding commands to the oai telnet server](telnetaddcmd.md)
+* [telnet server architecture ](telnetarch.md)
  
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