Configure libosmocore logging system as multithread

OsmoCBC uses libulfius, which creates its own thread(s).
Hence, we must set up osmocom logging system appropiately so that
relevant stuff is protected by locks.

Related: OS#5598
Change-Id: Ic06edc19d22b90e2b6b7de3a25d62cda5001f46e

src/cbc_main.c

@@ -212,6 +212,7 @@ int main(int argc, char **argv)
 	tall_rest_ctx = talloc_named_const(tall_cbc_ctx, 0, "REST");
 	msgb_talloc_ctx_init(tall_cbc_ctx, 0);
 	osmo_init_logging2(tall_cbc_ctx, &log_info);
+	log_enable_multithread();
 	osmo_stats_init(tall_cbc_ctx);
 	vty_init(&vty_info);