fix building under windows

net/net_windows.go

@@ -11,7 +11,7 @@ const (
 	AF_UNSPEC = windows.AF_UNSPEC
 
 	IPPROTO_IP   = windows.IPPROTO_IP
-	IPPROTO_IPV4 = windows.IPPROTO_IPV4
+	IPPROTO_IPV4 = 0x4 // windows.IPPROTO_IPV4 (missing)
 	IPPROTO_IPV6 = windows.IPPROTO_IPV6
 	IPPROTO_TCP  = windows.IPPROTO_TCP
 	IPPROTO_UDP  = windows.IPPROTO_UDP

sockaddr_windows.go

@@ -25,7 +25,7 @@ func sockaddrToAny(sa windows.Sockaddr) (*windows.RawSockaddrAny, Socklen, error
 		for i := 0; i < len(sa.Addr); i++ {
 			raw.Addr[i] = sa.Addr[i]
 		}
-		return (*windows.RawSockaddrAny)(unsafe.Pointer(&raw)), int32(unsafe.Sizeof(raw)), nil
+		return (*windows.RawSockaddrAny)(unsafe.Pointer(&raw)), Socklen(unsafe.Sizeof(raw)), nil
 
 	case *windows.SockaddrInet6:
 		if sa.Port < 0 || sa.Port > 0xFFFF {
@@ -40,7 +40,7 @@ func sockaddrToAny(sa windows.Sockaddr) (*windows.RawSockaddrAny, Socklen, error
 		for i := 0; i < len(sa.Addr); i++ {
 			raw.Addr[i] = sa.Addr[i]
 		}
-		return (*windows.RawSockaddrAny)(unsafe.Pointer(&raw)), int32(unsafe.Sizeof(raw)), nil
+		return (*windows.RawSockaddrAny)(unsafe.Pointer(&raw)), Socklen(unsafe.Sizeof(raw)), nil
 
 	case *windows.SockaddrUnix:
 		return nil, 0, syscall.EWINDOWS
@@ -50,7 +50,7 @@ func sockaddrToAny(sa windows.Sockaddr) (*windows.RawSockaddrAny, Socklen, error
 
 func anyToSockaddr(rsa *windows.RawSockaddrAny) (windows.Sockaddr, error) {
 	if rsa == nil {
-		return nil, 0, syscall.EINVAL
+		return nil, syscall.EINVAL
 	}
 
 	switch rsa.Addr.Family {