syscall: add IPv4 ancillary data for linux

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5039042

src/pkg/syscall/types_linux.c

@@ -117,6 +117,7 @@ typedef struct ip_mreq $IPMreq;
 typedef struct ipv6_mreq $IPv6Mreq;
 typedef struct msghdr $Msghdr;
 typedef struct cmsghdr $Cmsghdr;
+typedef struct in_pktinfo $Inet4Pktinfo;
 typedef struct in6_pktinfo $Inet6Pktinfo;
 typedef struct ucred $Ucred;
 
@@ -132,6 +133,7 @@ enum {
 	$SizeofIPv6Mreq = sizeof(struct ipv6_mreq),
 	$SizeofMsghdr = sizeof(struct msghdr),
 	$SizeofCmsghdr = sizeof(struct cmsghdr),
+	$SizeofInet4Pktinfo = sizeof(struct in_pktinfo),
 	$SizeofInet6Pktinfo = sizeof(struct in6_pktinfo),
 	$SizeofUcred = sizeof(struct ucred),
 };

src/pkg/syscall/ztypes_linux_386.go

@@ -23,6 +23,7 @@ const (
 	SizeofIPv6Mreq          = 0x14
 	SizeofMsghdr            = 0x1c
 	SizeofCmsghdr           = 0xc
+	SizeofInet4Pktinfo      = 0xc
 	SizeofInet6Pktinfo      = 0x14
 	SizeofUcred             = 0xc
 	IFA_UNSPEC              = 0
@@ -328,6 +329,12 @@ type Cmsghdr struct {
 	Type  int32
 }
 
+type Inet4Pktinfo struct {
+	Ifindex  int32
+	Spec_dst [4]byte /* in_addr */
+	Addr     [4]byte /* in_addr */
+}
+
 type Inet6Pktinfo struct {
 	Addr    [16]byte /* in6_addr */
 	Ifindex uint32

src/pkg/syscall/ztypes_linux_amd64.go

@@ -23,6 +23,7 @@ const (
 	SizeofIPv6Mreq          = 0x14
 	SizeofMsghdr            = 0x38
 	SizeofCmsghdr           = 0x10
+	SizeofInet4Pktinfo      = 0xc
 	SizeofInet6Pktinfo      = 0x14
 	SizeofUcred             = 0xc
 	IFA_UNSPEC              = 0
@@ -330,6 +331,12 @@ type Cmsghdr struct {
 	Type  int32
 }
 
+type Inet4Pktinfo struct {
+	Ifindex  int32
+	Spec_dst [4]byte /* in_addr */
+	Addr     [4]byte /* in_addr */
+}
+
 type Inet6Pktinfo struct {
 	Addr    [16]byte /* in6_addr */
 	Ifindex uint32

src/pkg/syscall/ztypes_linux_arm.go

@@ -28,6 +28,7 @@ const (
 	SizeofIPv6Mreq          = 0x14
 	SizeofMsghdr            = 0x1c
 	SizeofCmsghdr           = 0xc
+	SizeofInet4Pktinfo      = 0xc
 	SizeofInet6Pktinfo      = 0x14
 	SizeofUcred             = 0xc
 	IFA_UNSPEC              = 0
@@ -335,6 +336,12 @@ type Cmsghdr struct {
 	Type  int32
 }
 
+type Inet4Pktinfo struct {
+	Ifindex  int32
+	Spec_dst [4]byte /* in_addr */
+	Addr     [4]byte /* in_addr */
+}
+
 type Inet6Pktinfo struct {
 	Addr    [16]byte /* in6_addr */
 	Ifindex uint32