Reviewed and added OSX patch

The patch was provided by:
Naveen Nathan <naveen@lastninja.net>

The following modifications to the patch was made:

- Added copyright notice
- Fixed file descriptor leak in .MTU() method
- Migrated to the new(er) golang.org/x/sys/unix package
- Removed non-functioning Daemonize method

src/uapi_darwin.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"time"
+)
+
+/* TODO:
+ * This code can be improved by using fsnotify once:
+ * https://github.com/fsnotify/fsnotify/pull/205
+ * Is merged
+ */
+
+type UAPIListener struct {
+	listener net.Listener // unix socket listener
+	connNew  chan net.Conn
+	connErr  chan error
+}
+
+func (l *UAPIListener) Accept() (net.Conn, error) {
+	for {
+		select {
+		case conn := <-l.connNew:
+			return conn, nil
+
+		case err := <-l.connErr:
+			return nil, err
+		}
+	}
+}
+
+func (l *UAPIListener) Close() error {
+	return l.listener.Close()
+}
+
+func (l *UAPIListener) Addr() net.Addr {
+	return nil
+}
+
+func NewUAPIListener(name string) (net.Listener, error) {
+
+	// open UNIX socket
+
+	socketPath := fmt.Sprintf("/var/run/wireguard/%s.sock", name)
+	listener, err := net.Listen("unix", socketPath)
+	if err != nil {
+		return nil, err
+	}
+
+	uapi := &UAPIListener{
+		listener: listener,
+		connNew:  make(chan net.Conn, 1),
+		connErr:  make(chan error, 1),
+	}
+
+	// watch for deletion of socket
+
+	go func(l *UAPIListener) {
+		for ; ; time.Sleep(time.Second) {
+			if _, err := os.Stat(socketPath); os.IsNotExist(err) {
+				l.connErr <- err
+				return
+			}
+		}
+	}(uapi)
+
+	// watch for new connections
+
+	go func(l *UAPIListener) {
+		for {
+			conn, err := l.listener.Accept()
+			if err != nil {
+				l.connErr <- err
+				break
+			}
+			l.connNew <- conn
+		}
+	}(uapi)
+
+	return uapi, nil
+}