vty: don't store configurations for timeslots in mode NONE

This reflects what happens in libosmo-abis during 'show e1'
and makes sure we don't attempt to write for more TS than exist
(e.g. in the T1 case).

Change-Id: Iaeac2d080ae3ddc27901cbc4be5220100e9820a8
diff --git a/src/vty.c b/src/vty.c
index f0c8287..9dc548b 100644
--- a/src/vty.c
+++ b/src/vty.c
@@ -170,6 +170,9 @@
 		struct e1inp_ts *ts = &line->ts[i];
 		const char *mode_str;
 
+		if (ts->type == E1INP_TS_TYPE_NONE)
+			continue;
+
 		mode_str = get_value_string(e1inp_ts_type_names, ts->type);
 
 		vty_out(vty, " line %u ts %u mode %s%s",