plugin/cache: add minttl test (#1141)

See https://github.com/kubernetes/kubernetes/pull/53604, explicitaly add
test to make sure we do the right thing.

plugin/pkg/response/typify.go

@@ -99,8 +99,6 @@ func Typify(m *dns.Msg, t time.Time) (Type, *dns.OPT) {
 		}
 	}
 
-	// Check length of different sections, and drop stuff that is just to large? TODO(miek).
-
 	if soa && m.Rcode == dns.RcodeSuccess {
 		return NoData, opt
 	}