BUILD: sink: include tools.h in sink.c

Several functions from tools.h are used in sink.c without tools.h being
included.
diff --git a/src/sink.c b/src/sink.c
index 159c236..78091aa 100644
--- a/src/sink.c
+++ b/src/sink.c
@@ -30,6 +30,7 @@
 #include <haproxy/sink.h>
 #include <haproxy/stream_interface.h>
 #include <haproxy/time.h>
+#include <haproxy/tools.h>
 
 struct list sink_list = LIST_HEAD_INIT(sink_list);