windows: add cmsghdr and pktinfo structures

- CMSGHDR from ws2def.h, corresponds to Cmsghdr in unix
- IN_PKTINFO from ws2ipdef.h, corresponds to InetPktinfo in unix
- IN6_PKTINFO from ws2ipdef.h, corresponds to Inet6Pktinfo in unix

Change-Id: I74f6812588859c3a6080e6675df28998fc435965
GitHub-Last-Rev: 7377c79
GitHub-Pull-Request: #246
Reviewed-on: https://go-review.googlesource.com/c/sys/+/658175
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

Author: database64128

windows/types_windows.go

@@ -1157,6 +1157,22 @@ type WSAMsg struct {
 	Flags       uint32
 }
 
+type WSACMSGHDR struct {
+	Len   uintptr
+	Level int32
+	Type  int32
+}
+
+type IN_PKTINFO struct {
+	Addr    [4]byte
+	Ifindex uint32
+}
+
+type IN6_PKTINFO struct {
+	Addr    [16]byte
+	Ifindex uint32
+}
+
 // Flags for WSASocket
 const (
 	WSA_FLAG_OVERLAPPED             = 0x01