plugin/cache: Unset AD flag when DO is not set for cache miss (#4736)

* unset AD bit when client DO is 0

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* add flag check to existing tests

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/test/helpers.go

@@ -29,14 +29,15 @@ func (p RRSet) Less(i, j int) bool { return p[i].String() < p[j].String() }
 // Case represents a test case that encapsulates various data from a query and response.
 // Note that is the TTL of a record is 303 we don't compare it with the TTL.
 type Case struct {
-	Qname  string
-	Qtype  uint16
-	Rcode  int
-	Do     bool
-	Answer []dns.RR
-	Ns     []dns.RR
-	Extra  []dns.RR
-	Error  error
+	Qname             string
+	Qtype             uint16
+	Rcode             int
+	Do                bool
+	AuthenticatedData bool
+	Answer            []dns.RR
+	Ns                []dns.RR
+	Extra             []dns.RR
+	Error             error
 }
 
 // Msg returns a *dns.Msg embedded in c.