Move timezone settings up to network level

Time zone used to be configurable per-BTS. In the upcoming MSC-split, no BTS
structures will be available on the MSC level. To simplify, drop the ability to
manage several time zones in a core network and place the time zone config on
the network VTY level, i.e. in gsm_network. If we are going to re-add fine
grained time zone settings, it should probably be tied to the LAC.

Adjust time zone VTY config code (to be moved to libcommon-cs in subsequent commit).

Adjust time zone Ctrl Interface code.

Change-Id: I69848887d92990f3d6f969be80f6ef91f6bdbbe8
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_filter.c b/openbsc/src/osmo-bsc/osmo_bsc_filter.c
index 66c6406..d5ca2fd 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_filter.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_filter.c
@@ -270,23 +270,24 @@
 		return 0;
 
 	/* Is TZ patching enabled? */
-	if (!bts->tz.override)
+	struct gsm_tz *tz = &bts->network->tz;
+	if (!tz->override)
 		return 0;
 
 	/* Convert tz.hr and tz.mn to units */
-	if (bts->tz.hr < 0) {
-		tzunits = -bts->tz.hr*4;
+	if (tz->hr < 0) {
+		tzunits = -tz->hr*4;
 		tzbsd |= 0x08;
 	} else
-		tzunits = bts->tz.hr*4;
+		tzunits = tz->hr*4;
 
-	tzunits = tzunits + (bts->tz.mn/15);
+	tzunits = tzunits + (tz->mn/15);
 
 	tzbsd |= (tzunits % 10)*0x10 + (tzunits / 10);
 
 	/* Convert DST value */
-	if (bts->tz.dst >= 0 && bts->tz.dst <= 2)
-		dst = bts->tz.dst;
+	if (tz->dst >= 0 && tz->dst <= 2)
+		dst = tz->dst;
 
 	if (TLVP_PRESENT(&tp, GSM48_IE_UTC)) {
 		LOGP(DMSC, LOGL_DEBUG,