vendor: add kcp-go package

vendor/golang.org/x/net/ipv4/bpfopt_linux.go

@@ -0,0 +1,27 @@
+// Copyright 2016 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 (
+	"os"
+	"unsafe"
+
+	"golang.org/x/net/bpf"
+)
+
+// SetBPF attaches a BPF program to the connection.
+//
+// Only supported on Linux.
+func (c *dgramOpt) SetBPF(filter []bpf.RawInstruction) error {
+	fd, err := c.sysfd()
+	if err != nil {
+		return err
+	}
+	prog := sysSockFProg{
+		Len:    uint16(len(filter)),
+		Filter: (*sysSockFilter)(unsafe.Pointer(&filter[0])),
+	}
+	return os.NewSyscallError("setsockopt", setsockopt(fd, sysSOL_SOCKET, sysSO_ATTACH_FILTER, unsafe.Pointer(&prog), uint32(unsafe.Sizeof(prog))))
+}