use osmo_init_logging2() with proper talloc ctx

There is a duality of initialization: early_init() in bts.cpp wants to init
logging even before static instances get initialized. Make sure that
tall_pcu_ctx is initialized during early_init() as well. There is a build
context that does not seem to include bts.cpp (osmo-pcu-remote), so to be sure,
init tall_pcu_ctx as NULL and both in early_init() as well as pcu_main.cpp,
init both tall_pcu_ctx and logging if it is still NULL.

Change-Id: I2199b62d0270bd35dec2283e8f5b364b7c63915b
diff --git a/src/bts.cpp b/src/bts.cpp
index 47607df..b6d0d0c 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -59,7 +59,10 @@
 	 * require logging already to be initialized. */
 	__attribute__((constructor)) static void early_init(void)
 	{
-		osmo_init_logging(&gprs_log_info);
+		if (!tall_pcu_ctx) {
+			tall_pcu_ctx = talloc_named_const(NULL, 1, "Osmo-PCU context");
+			osmo_init_logging2(tall_pcu_ctx, &gprs_log_info);
+		}
 	}
 }