vty: allow configuring db path from cfg file

So far, the cmdline argument was the only way to set a database file.
Add a similar config to VTY as 'msc' / 'sms-database'. The cmdline arg is stronger
than the 'database' cfg item. DB is not reloaded from VTY command.

Change-Id: I18d954c30fcceb0b36a620b927fd3a93dcc79f49
diff --git a/src/libmsc/msc_net_init.c b/src/libmsc/msc_net_init.c
index adb9ca7..774c767 100644
--- a/src/libmsc/msc_net_init.c
+++ b/src/libmsc/msc_net_init.c
@@ -61,6 +61,8 @@
 	if (!net)
 		return NULL;
 
+	net->sms_db_file_path = talloc_strdup(net, SMS_DEFAULT_DB_FILE_PATH);
+
 	net->plmn = (struct osmo_plmn_id){ .mcc=1, .mnc=1 };
 
 	/* Permit a compile-time default of A5/3 and A5/1 */