server: remove connection limit from tcl and telnet servers

Add constant CONNECTION_LIMIT_UNLIMITED which indicates a service
has no connection limit

Change-Id: I008d31264010c25fa44ca74eb6d5740eca38bee1
Signed-off-by: Austin Morton <austinpmorton@gmail.com>
Reviewed-on: http://openocd.zylin.com/2937
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>

src/server/server.h

@@ -39,6 +39,8 @@ enum connection_type {
 	CONNECTION_STDINOUT
 };
 
+#define CONNECTION_LIMIT_UNLIMITED		(-1)
+
 struct connection {
 	int fd;
 	int fd_out;	/* When using pipes we're writing to a different fd */