MINOR: sink: Add a ref to sink in the sink_forward_target structure

This change is required to be able to refactor the init stage of appctx. It
is now possible to directly get the sink from a forward target.

include/haproxy/sink-t.h

@@ -40,6 +40,7 @@ struct sink_forward_target {
 	struct server *srv;    // used server
 	struct appctx *appctx; // appctx of current session
 	size_t ofs;            // ring buffer reader offset
+	struct sink *sink;     // the associated sink
 	struct sink_forward_target *next;
 	__decl_thread(HA_SPINLOCK_T lock); // lock to protect current struct
 };

src/sink.c

@@ -1005,6 +1005,7 @@ struct sink *sink_new_from_logsrv(struct logsrv *logsrv)
 	/* insert into sink_forward_targets
 	 * list into sink
 	 */
+	sft->sink = sink;
 	sft->next = sink->sft;
 	sink->sft = sft;