internal/socket: add support for darwin/arm64

Fixes golang/go#22301.

Change-Id: I29f4f8806e10aad59cf7f984fd346acc216b0fd0
Reviewed-on: https://go-review.googlesource.com/79855
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

internal/socket/zsys_darwin_arm64.go

+// Created by cgo -godefs - DO NOT EDIT
+// cgo -godefs defs_darwin.go
+
+package socket
+
+const (
+	sysAF_UNSPEC = 0x0
+	sysAF_INET   = 0x2
+	sysAF_INET6  = 0x1e
+
+	sysSOCK_RAW = 0x3
+)
+
+type iovec struct {
+	Base *byte
+	Len  uint64
+}
+
+type msghdr struct {
+	Name       *byte
+	Namelen    uint32
+	Pad_cgo_0  [4]byte
+	Iov        *iovec
+	Iovlen     int32
+	Pad_cgo_1  [4]byte
+	Control    *byte
+	Controllen uint32
+	Flags      int32
+}
+
+type cmsghdr struct {
+	Len   uint32
+	Level int32
+	Type  int32
+}
+
+type sockaddrInet struct {
+	Len    uint8
+	Family uint8
+	Port   uint16
+	Addr   [4]byte /* in_addr */
+	Zero   [8]int8
+}
+
+type sockaddrInet6 struct {
+	Len      uint8
+	Family   uint8
+	Port     uint16
+	Flowinfo uint32
+	Addr     [16]byte /* in6_addr */
+	Scope_id uint32
+}
+
+const (
+	sizeofIovec   = 0x10
+	sizeofMsghdr  = 0x30
+	sizeofCmsghdr = 0xc
+
+	sizeofSockaddrInet  = 0x10
+	sizeofSockaddrInet6 = 0x1c
+)