MINOR: connection: add a new list member in the connection struct

This list member will be used to attach a connection to a list of
idle, reusable or queued connections. It's unused for now. Given
that it's not expected to be used more than a few times per session,
the member was put after the target, in the area starting at the
second cache line of the structure.

include/proto/connection.h

@@ -481,6 +481,7 @@ static inline void conn_init(struct connection *conn)
 	conn->err_code = CO_ER_NONE;
 	conn->target = NULL;
 	conn->proxy_netns = NULL;
+	LIST_INIT(&conn->list);
 }
 
 /* Tries to allocate a new connection and initialized its main fields. The

include/types/connection.h

@@ -261,6 +261,7 @@ struct connection {
 		} sock;
 	} t;
 	enum obj_type *target;        /* the target to connect to (server, proxy, applet, ...) */
+	struct list list;             /* attach point to various connection lists (idle, ...) */
 	const struct netns_entry *proxy_netns;
 	struct {
 		struct sockaddr_storage from;	/* client address, or address to spoof when connecting to the server */