ipdbg: split ipdbg command into multiple commands

To simplify the ipdbg start/stop command and be able to
add additional commands in the future, we introduce the
concept of a hub which has to be created before a
ipdbg server can be started.
The hub was created on the fly in previous versions.

Change-Id: I55f317542d01a7324990b2cacd496a41fa5ff875
Signed-off-by: Daniel Anselmi <danselmi@gmx.ch>
Reviewed-on: https://review.openocd.org/c/openocd/+/7979
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins

src/server/server.c

@@ -23,6 +23,7 @@
 #include "openocd.h"
 #include "tcl_server.h"
 #include "telnet_server.h"
+#include "ipdbg.h"
 
 #include <signal.h>
 
@@ -714,6 +715,7 @@ void server_free(void)
 	tcl_service_free();
 	telnet_service_free();
 	jsp_service_free();
+	ipdbg_server_free();
 
 	free(bindto_name);
 }