Import the new logging architecture

This is the new logging architecture, including

* support for multiuple logging targets like stderr and vty
* log levels in addition to categories/subsystems
* filtering based on imsi, i.e. only see events for one subscriber
* dynamically change log level for each category for each vty
diff --git a/openbsc/src/telnet_interface.c b/openbsc/src/telnet_interface.c
index bc91ca3..ebddaf5 100644
--- a/openbsc/src/telnet_interface.c
+++ b/openbsc/src/telnet_interface.c
@@ -120,6 +120,12 @@
 
 	close(fd->fd);
 	bsc_unregister_fd(fd);
+
+	if (conn->dbg) {
+		debug_del_target(conn->dbg);
+		talloc_free(conn->dbg);
+	}
+
 	llist_del(&conn->entry);
 	talloc_free(conn);
 	return 0;