BUG/MINOR: ssl: leak of ckch_inst_link in ckch_inst_free()

ckch_inst_free() unlink the ckch_inst_link structure but never free it.
It can cause a memory leak upon a ckch_inst_free() done with CLI
operation.

Bug introduced by commit 4458b97 ("MEDIUM: ssl: Chain ckch instances in
ca-file entries").

Must be backported as far as 2.5.

src/ssl_ckch.c

@@ -989,6 +989,7 @@ void ckch_inst_free(struct ckch_inst *inst)
 	list_for_each_entry_safe(link_ref, link_ref_s, &inst->cafile_link_refs, list) {
 		LIST_DELETE(&link_ref->link->list);
 		LIST_DELETE(&link_ref->list);
+		free(link_ref->link);
 		free(link_ref);
 	}