go.net/ipv4: fix openbsd build

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/149690043

ipv4/sys_bsd.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build dragonfly netbsd openbsd
+// +build dragonfly netbsd
 
 package ipv4
 

ipv4/sys_openbsd.go

@@ -0,0 +1,34 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ipv4
+
+import (
+	"net"
+	"syscall"
+)
+
+type sysSockoptLen int32
+
+var (
+	ctlOpts = [ctlMax]ctlOpt{
+		ctlTTL:       {sysIP_RECVTTL, 1, marshalTTL, parseTTL},
+		ctlDst:       {sysIP_RECVDSTADDR, net.IPv4len, marshalDst, parseDst},
+		ctlInterface: {sysIP_RECVIF, syscall.SizeofSockaddrDatalink, marshalInterface, parseInterface},
+	}
+
+	sockOpts = [ssoMax]sockOpt{
+		ssoTOS:                {sysIP_TOS, ssoTypeInt},
+		ssoTTL:                {sysIP_TTL, ssoTypeInt},
+		ssoMulticastTTL:       {sysIP_MULTICAST_TTL, ssoTypeByte},
+		ssoMulticastInterface: {sysIP_MULTICAST_IF, ssoTypeInterface},
+		ssoMulticastLoopback:  {sysIP_MULTICAST_LOOP, ssoTypeByte},
+		ssoReceiveTTL:         {sysIP_RECVTTL, ssoTypeInt},
+		ssoReceiveDst:         {sysIP_RECVDSTADDR, ssoTypeInt},
+		ssoReceiveInterface:   {sysIP_RECVIF, ssoTypeInt},
+		ssoHeaderPrepend:      {sysIP_HDRINCL, ssoTypeInt},
+		ssoJoinGroup:          {sysIP_ADD_MEMBERSHIP, ssoTypeIPMreq},
+		ssoLeaveGroup:         {sysIP_DROP_MEMBERSHIP, ssoTypeIPMreq},
+	}
+)