BUG/MINOR: resolvers: Use sc_need_room() to wait more room when dumping stats

It was a cut/paste typo during stream-interface to conn-stream
refactoring. sc_have_room() was used instead of sc_need_room().

This patch must be backported as far as 2.6.

src/resolvers.c

@@ -2693,7 +2693,7 @@ static int stats_dump_resolv_to_buffer(struct stconn *sc,
 	return 1;
 
   full:
-	sc_have_room(sc);
+	sc_need_room(sc);
 	return 0;
 }