stub out more types/funcs to compile against golang.org/x/net/internal/socket (#17)

* stub out more types/funcs to compile against golang.org/x/net/internal/socket

These are changes need to compile github.com/domainr/dnsr/ with TinyGo. See issue tinygo-org/net#14.

These change are mostly to fix missing symbols in src/net. Missing types and functions are cut-and-pasted from go1.21.4. Functions are stubbed out returning errors.New("not implemented").

DNRS is compiled by running tinygo test:

   sfeldma@nuc:~/work/dnsr$ tinygo test -target=wasi

With this patch, and a corresponding patch for tinygo/ to fixup crypto/tls, you should get a clean compile.

unixsock.go

@@ -0,0 +1,43 @@
+// TINYGO: The following is copied and modified from Go 1.21.4 official implementation.
+
+// Copyright 2009 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 net
+
+// BUG(mikio): On JS, WASIP1 and Plan 9, methods and functions related
+// to UnixConn and UnixListener are not implemented.
+
+// BUG(mikio): On Windows, methods and functions related to UnixConn
+// and UnixListener don't work for "unixgram" and "unixpacket".
+
+// UnixAddr represents the address of a Unix domain socket end point.
+type UnixAddr struct {
+	Name string
+	Net  string
+}
+
+// Network returns the address's network name, "unix", "unixgram" or
+// "unixpacket".
+func (a *UnixAddr) Network() string {
+	return a.Net
+}
+
+func (a *UnixAddr) String() string {
+	if a == nil {
+		return "<nil>"
+	}
+	return a.Name
+}
+
+func (a *UnixAddr) isWildcard() bool {
+	return a == nil || a.Name == ""
+}
+
+func (a *UnixAddr) opAddr() Addr {
+	if a == nil {
+		return nil
+	}
+	return a
+}