MINOR: http: add array of generic pointers in http_res_rules

This patch adds an array of generic pointers in the http_res_rules
struct. It is used later by the "response capture" functions.

include/types/proto_http.h

@@ -477,6 +477,9 @@ struct http_res_rule {
 			struct list key;       /* pattern to retrieve MAP or ACL key */
 			struct list value;     /* pattern to retrieve MAP value */
 		} map;
+		struct {
+			void *p[4];
+		} act;                         /* generic pointers to be used by custom actions */
 	} arg;                                 /* arguments used by some actions */
 };