move talloc context creation out of on_dso / constructors

the various constructors get called in a non-obvious, linker determined
order, which makes certain objects disappear from the talloc report.

This change moves the talloc context creation into a new talloc_ctx.c file
diff --git a/openbsc/src/gsm_04_08.c b/openbsc/src/gsm_04_08.c
index dc2bd19..e5ab49d 100644
--- a/openbsc/src/gsm_04_08.c
+++ b/openbsc/src/gsm_04_08.c
@@ -56,7 +56,7 @@
 #define GSM_MAX_SSVERSION      128
 #define GSM_MAX_USERUSER       128
 
-static void *tall_locop_ctx;
+void *tall_locop_ctx;
 
 /* should ip.access BTS use direct RTP streams between each other (1),
  * or should OpenBSC always act as RTP relay/proxy in between (0) ? */
@@ -3896,8 +3896,6 @@
  */
 static __attribute__((constructor)) void on_dso_load_0408(void)
 {
-	tall_locop_ctx = talloc_named_const(tall_bsc_ctx, 1,
-					    "loc_updating_oper");
 	register_signal_handler(SS_LCHAN, gsm0408_handle_lchan_signal, NULL);
 	register_signal_handler(SS_ABISIP, handle_abisip_signal, NULL);
 }