VTY: add osmo_tdef introspection and configuration commands

This change introduces several new VTY commands letting the user
a possibility to introspect and reconfigure some of the existing
timers implemented using libosmocore's osmo_tdef API.

At the moment this covers the following timers:

  - MGW specific timers:
    - X1 - MGCP response timeout,
    - X2 - RTP stream establishing timeout,

  - RAN specific timers (same names for GERAN and UTRAN):
    - X1 - Authentication and Ciphering timeout,
    - X2 - RAN connection release sanity timeout,
    - X3 - Handover procedure timeout.

The following commands are introduced:

  - 'enable' node:
    - show timer [(mgw|mncc|sccp|geran|utran|sgs)] [TNNNN]

  - 'config-msc' node:
    - timer [(mgw|mncc|sccp|geran|utran|sgs)] [TNNNN] [(<0-2147483647>|default)]

Both MNCC and SCCP related timer definitions are empty at the
moment. Achieved by using osmo_tdef_group API of libosmovty.

Change-Id: I6024c104b6101666c8aa1108a043910eb75db9a5
Related: OS#4368
diff --git a/include/osmocom/msc/msc_common.h b/include/osmocom/msc/msc_common.h
index 78337f7..bd85722 100644
--- a/include/osmocom/msc/msc_common.h
+++ b/include/osmocom/msc/msc_common.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <osmocom/core/tdef.h>
+
 #include <osmocom/gsm/protocol/gsm_04_08.h>
 #include <osmocom/gsm/gsm0808.h>
 
@@ -7,6 +9,8 @@
 struct gsm_network;
 struct vlr_subscr;
 
+extern struct osmo_tdef_group msc_tdef_group[];
+
 #define MSC_HLR_REMOTE_IP_DEFAULT "127.0.0.1"
 #define MSC_HLR_REMOTE_PORT_DEFAULT OSMO_GSUP_PORT