mobile/main.c: fix deprecated call to msgb_set_talloc_ctx()

The usage of msgb_set_talloc_ctx() was deprecated many days ago,
so it's time to use the proper replacement.

Change-Id: I56440d8e2152c4bb2e5ad677f88c61742d2ad9ca

src/host/layer23/src/mobile/main.c

@@ -220,7 +220,8 @@ int main(int argc, char **argv)
 	log_set_all_filter(stderr_target, 1);
 
 	l23_ctx = talloc_named_const(NULL, 1, "layer2 context");
-	msgb_set_talloc_ctx(l23_ctx);
+	/* TODO: measure and choose a proper pool size */
+	msgb_talloc_ctx_init(l23_ctx, 0);
 
 	handle_options(argc, argv);