[MINOR] stick_table: provide functions to return stksess data from a type

This function does the indirection job in the table to find the pointer
to the real data matching the requested type.
diff --git a/include/proto/stick_table.h b/include/proto/stick_table.h
index 4200d97..e1a324d 100644
--- a/include/proto/stick_table.h
+++ b/include/proto/stick_table.h
@@ -25,6 +25,9 @@
 
 #include <types/stick_table.h>
 
+#define stktable_data_size(type) (sizeof(((union stktable_data*)0)->type))
+#define stktable_data_cast(ptr, type) ((union stktable_data*)(ptr))->type
+
 struct stksess *stksess_new(struct stktable *t, struct stktable_key *key);
 void stksess_setkey(struct stktable *t, struct stksess *ts, struct stktable_key *key);
 void stksess_free(struct stktable *t, struct stksess *ts);
@@ -57,4 +60,21 @@
 	return 1;
 }
 
+/* return pointer for data type <type> in sticky session <ts> of table <t>, or
+ * NULL if either <ts> is NULL or the type is not stored.
+ */
+static inline void *stktable_data_ptr(struct stktable *t, struct stksess *ts, int type)
+{
+	if (type >= STKTABLE_DATA_TYPES)
+		return NULL;
+
+	if (!t->data_ofs[type]) /* type not stored */
+		return NULL;
+
+	if (!ts)
+		return NULL;
+
+	return (void *)ts + t->data_ofs[type];
+}
+
 #endif /* _PROTO_STICK_TABLE_H */