BUILD: mworker: include tools.h from mworker.c

It needs it for memprintf() but didn't include the file.
diff --git a/src/mworker.c b/src/mworker.c
index b69c1ad..4819d16 100644
--- a/src/mworker.c
+++ b/src/mworker.c
@@ -37,6 +37,7 @@
 #include <haproxy/signal.h>
 #include <haproxy/stream.h>
 #include <haproxy/stream_interface.h>
+#include <haproxy/tools.h>
 #include <haproxy/version.h>