net: remove unneeded tags from dnsRR structs

DNS packing and unpacking uses hand-coded struct walking functions
rather than reflection, so these tags are unneeded and just contribute
to their runtime reflect metadata size.

Change-Id: I2db09d5159912bcbc3b482cbf23a50fa8fa807fa
Reviewed-on: https://go-review.googlesource.com/22594
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/dnsmsg.go

@@ -109,7 +109,7 @@ const (
 
 // DNS queries.
 type dnsQuestion struct {
-	Name   string `net:"domain-name"` // `net:"domain-name"` specifies encoding; see packers below
+	Name   string
 	Qtype  uint16
 	Qclass uint16
 }
@@ -124,7 +124,7 @@ func (q *dnsQuestion) Walk(f func(v interface{}, name, tag string) bool) bool {
 // There are many types of messages,
 // but they all share the same header.
 type dnsRR_Header struct {
-	Name     string `net:"domain-name"`
+	Name     string
 	Rrtype   uint16
 	Class    uint16
 	Ttl      uint32
@@ -152,7 +152,7 @@ type dnsRR interface {
 
 type dnsRR_CNAME struct {
 	Hdr   dnsRR_Header
-	Cname string `net:"domain-name"`
+	Cname string
 }
 
 func (rr *dnsRR_CNAME) Header() *dnsRR_Header {
@@ -166,7 +166,7 @@ func (rr *dnsRR_CNAME) Walk(f func(v interface{}, name, tag string) bool) bool {
 type dnsRR_MX struct {
 	Hdr  dnsRR_Header
 	Pref uint16
-	Mx   string `net:"domain-name"`
+	Mx   string
 }
 
 func (rr *dnsRR_MX) Header() *dnsRR_Header {
@@ -179,7 +179,7 @@ func (rr *dnsRR_MX) Walk(f func(v interface{}, name, tag string) bool) bool {
 
 type dnsRR_NS struct {
 	Hdr dnsRR_Header
-	Ns  string `net:"domain-name"`
+	Ns  string
 }
 
 func (rr *dnsRR_NS) Header() *dnsRR_Header {
@@ -192,7 +192,7 @@ func (rr *dnsRR_NS) Walk(f func(v interface{}, name, tag string) bool) bool {
 
 type dnsRR_PTR struct {
 	Hdr dnsRR_Header
-	Ptr string `net:"domain-name"`
+	Ptr string
 }
 
 func (rr *dnsRR_PTR) Header() *dnsRR_Header {
@@ -205,8 +205,8 @@ func (rr *dnsRR_PTR) Walk(f func(v interface{}, name, tag string) bool) bool {
 
 type dnsRR_SOA struct {
 	Hdr     dnsRR_Header
-	Ns      string `net:"domain-name"`
-	Mbox    string `net:"domain-name"`
+	Ns      string
+	Mbox    string
 	Serial  uint32
 	Refresh uint32
 	Retry   uint32
@@ -263,7 +263,7 @@ type dnsRR_SRV struct {
 	Priority uint16
 	Weight   uint16
 	Port     uint16
-	Target   string `net:"domain-name"`
+	Target   string
 }
 
 func (rr *dnsRR_SRV) Header() *dnsRR_Header {
@@ -280,7 +280,7 @@ func (rr *dnsRR_SRV) Walk(f func(v interface{}, name, tag string) bool) bool {
 
 type dnsRR_A struct {
 	Hdr dnsRR_Header
-	A   uint32 `net:"ipv4"`
+	A   uint32
 }
 
 func (rr *dnsRR_A) Header() *dnsRR_Header {
@@ -293,7 +293,7 @@ func (rr *dnsRR_A) Walk(f func(v interface{}, name, tag string) bool) bool {
 
 type dnsRR_AAAA struct {
 	Hdr  dnsRR_Header
-	AAAA [16]byte `net:"ipv6"`
+	AAAA [16]byte
 }
 
 func (rr *dnsRR_AAAA) Header() *dnsRR_Header {