MINOR: logs: Use dedicated function to init/deinit log buffers

Now, we use init_log_buffers and deinit_log_buffers to, respectively, initialize
and deinitialize log buffers used for syslog messages.

These functions have been introduced to be used by threads, to deal with
thread-local log buffers.
diff --git a/src/haproxy.c b/src/haproxy.c
index efc4da5..7c925ea 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -2107,6 +2107,7 @@
 
 	cfg_unregister_sections();
 
+	deinit_log_buffers();
 	deinit_trash_buffers();
 
 	protocol_unbind_all();