main, tests: use msgb_talloc_ctx_init() (new)

msgb_set_talloc_ctx() is deprecated since libosmocore commit
f45334be29016a36594aacc07c90e262e4994525 / change-id
I747fbbf977c4d2c868c8dead64cfc5fd86eb8d4c

Change-Id: I8d40abec428b739460ed545c9983d1b63021bd08
diff --git a/src/pcu_main.cpp b/src/pcu_main.cpp
index 0a0362b..338096b 100644
--- a/src/pcu_main.cpp
+++ b/src/pcu_main.cpp
@@ -217,7 +217,7 @@
 	 */
 	bts->dl_arq_type = EGPRS_ARQ1;
 
-	msgb_set_talloc_ctx(tall_pcu_ctx);
+	msgb_talloc_ctx_init(tall_pcu_ctx, 0);
 
 	osmo_init_logging(&gprs_log_info);
 	osmo_stats_init(tall_pcu_ctx);