Link refactor (#941)

* Link refactoring

* More refactoring

* More tweaking

* Cleaner shutdowns, UNIX socket support, more tweaks

* Actorise links, remove mutex

* SOCKS support

src/core/tcp_darwin.go

@@ -1,33 +0,0 @@
-//go:build darwin
-// +build darwin
-
-package core
-
-import (
-	"syscall"
-
-	"golang.org/x/sys/unix"
-)
-
-// WARNING: This context is used both by net.Dialer and net.Listen in tcp.go
-
-func (t *tcp) tcpContext(network, address string, c syscall.RawConn) error {
-	var control error
-	var recvanyif error
-
-	control = c.Control(func(fd uintptr) {
-		// sys/socket.h: #define	SO_RECV_ANYIF	0x1104
-		recvanyif = unix.SetsockoptInt(int(fd), syscall.SOL_SOCKET, 0x1104, 1)
-	})
-
-	switch {
-	case recvanyif != nil:
-		return recvanyif
-	default:
-		return control
-	}
-}
-
-func (t *tcp) getControl(sintf string) func(string, string, syscall.RawConn) error {
-	return t.tcpContext
-}