MINOR: debug: Add check for CO_FL_WILL_UPDATE

This could be backported to 1.8.
diff --git a/contrib/debug/flags.c b/contrib/debug/flags.c
index 558072f..959d251 100644
--- a/contrib/debug/flags.c
+++ b/contrib/debug/flags.c
@@ -135,6 +135,7 @@
 	SHOW_FLAG(f, CO_FL_ADDR_TO_SET);
 	SHOW_FLAG(f, CO_FL_ADDR_FROM_SET);
 	SHOW_FLAG(f, CO_FL_WAIT_ROOM);
+	SHOW_FLAG(f, CO_FL_WILL_UPDATE);
 	SHOW_FLAG(f, CO_FL_XPRT_READY);
 	SHOW_FLAG(f, CO_FL_CTRL_READY);
 	SHOW_FLAG(f, CO_FL_CURR_WR_ENA);