Fix MS TO measurement representation

* set proper flag when saving MS Timing Offset
* use gsm_subscriber's IMSI or lchan's name if bsc_subscriber is unknown
* add comments with spec reference
* store/display MS Timing Offset instead of raw Timing Offset field from
  RSL
* Compute MS Timing Offset [-63; 192] from Timing Offset field [0; 255],
  adjust structure gsm_meas_rep with proper type to store it

Change-Id: I7e003d23a6edb714c5f17688fd6a8edac131161d
Related: OS#1574
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index c1882fc..3c70580 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -1062,8 +1062,7 @@
 			mr->flags & MEAS_REP_F_DL_VALID ? " " : "DLinval ",
 			VTY_NEWLINE);
 	if (mr->flags & MEAS_REP_F_MS_TO)
-		vty_out(vty, "%s  MS Timing Offset: %u%s", prefix,
-			mr->ms_timing_offset, VTY_NEWLINE);
+		vty_out(vty, "%s  MS Timing Offset: %d%s", prefix, mr->ms_timing_offset, VTY_NEWLINE);
 	if (mr->flags & MEAS_REP_F_MS_L1)
 		vty_out(vty, "%s  L1 MS Power: %u dBm, Timing Advance: %u%s",
 			prefix, mr->ms_l1.pwr, mr->ms_l1.ta, VTY_NEWLINE);