fix(dnssec): change EDNS0 UDP buffer size to 1232 as per the current recommendation

common/dnssec/walker_iterative.go

@@ -29,7 +29,7 @@ func (w *iterativeWalker) resetStats()            { w.st = ValidationStats{} }
 func (w *iterativeWalker) exchange(server, name string, qtype uint16) (*dns.Msg, error) {
 	m := new(dns.Msg)
 	m.SetQuestion(dns.Fqdn(name), qtype)
-	m.SetEdns0(4096, true)
+	m.SetEdns0(1232, true)
 	m.RecursionDesired = false
 
 	if b, err := m.Pack(); err == nil {

common/dnssec/walker_trust.go

@@ -24,7 +24,7 @@ func (w *trustWalker) ask(name string, qtype uint16) (*dns.Msg, error) {
 	m.SetQuestion(dns.Fqdn(name), qtype)
 	m.Id = dns.Id()
 	m.RecursionDesired = true
-	m.SetEdns0(4096, true)
+	m.SetEdns0(1232, true)
 
 	if b, err := m.Pack(); err == nil {
 		w.st.BytesSent += len(b)