Make request.Request smaller (#3351)

* Make request.Request smaller

This makes the request struct smaller and removes the pointer to the do
boolean (tri-bool) as size == 0 will indicate if we have cached it.

Family can be a int8 because it only carries 3 values, Size itself is
just a uint16 under the covers.

This is a more comprehensive fix than #3292

Closes #3292

Signed-off-by: Miek Gieben <miek@miek.nl>

* cache: fix test

this now needs a valid response writter

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/cache/cache_test.go

@@ -191,7 +191,7 @@ func TestCache(t *testing.T) {
 		m := tc.in.Msg()
 		m = cacheMsg(m, tc)
 
-		state := request.Request{W: nil, Req: m}
+		state := request.Request{W: &test.ResponseWriter{}, Req: m}
 
 		mt, _ := response.Typify(m, utc)
 		valid, k := key(state.Name(), m, mt, state.Do())