MINOR: action: add reference to the original keywork matched for the called parser.

This is usefull because the keyword can contains some condifiguration
data set while the keyword registration.
diff --git a/include/types/action.h b/include/types/action.h
index d74e5ba..b7e1063 100644
--- a/include/types/action.h
+++ b/include/types/action.h
@@ -93,6 +93,7 @@
 	short deny_status;                     /* HTTP status to return to user when denying */
 	enum act_return (*action_ptr)(struct act_rule *rule, struct proxy *px,
 	                              struct session *sess, struct stream *s); /* ptr to custom action */
+	struct action_kw *kw;
 	union {
 		struct {
 			char *realm;