sms: Give smsc its own VTY config node

The pre-historic sms_queue code used to have very strange aspects,
such as having some parameters (max-failure, max-pending) which could
only be sent from the 'enable' node, but not from a config file.

Before adding more configuration parameters, let's clean this up by
introducing a proper VTY config node for the 'smsc'; move the existing
config commands there and add new ones for max-failure and max-pending.

As the sms_queue data structure is only allocated after the config file
parsing happens, we are introducing a new 'sms_queue_config' data
structure.  This encapsulates the public readable/writable config
parameters.

Change-Id: Ie8e0ab1a9f979337ff06544b9ab3820954d9804a
diff --git a/include/osmocom/msc/vty.h b/include/osmocom/msc/vty.h
index 2a3b18b..1e13846 100644
--- a/include/osmocom/msc/vty.h
+++ b/include/osmocom/msc/vty.h
@@ -24,11 +24,13 @@
 	SMPP_ESME_NODE,
 	HLR_NODE,
 	CFG_SGS_NODE,
+	SMSC_NODE,
 };
 
 int bsc_vty_init_extra(void);
 
 void msc_vty_init(struct gsm_network *msc_network);
+void smsc_vty_init(struct gsm_network *msc_network);
 
 struct gsm_network *gsmnet_from_vty(struct vty *vty);