BUG/MEDIUM: sink: Set the sink ref for forwarders created during ring parsing

A reference to the sink was added in every forwarder by the commit 2ae25ea24
("MINOR: sink: Add a ref to sink in the sink_forward_target structure"). But
this commit is incomplete. It is not performed for the forwarders created
during a ring parsing.

This patch must be backported to 2.6.

src/sink.c

@@ -1102,6 +1102,7 @@ int cfg_post_parse_ring()
 				sft->srv = srv;
 				sft->appctx = NULL;
 				sft->ofs = ~0; /* init ring offset */
+				sft->sink = cfg_sink;
 				sft->next = cfg_sink->sft;
 				HA_SPIN_INIT(&sft->lock);