Merge pull request ARMmbed#21 from syoder/flush-socket-after-bind

After binding to the HCI socket, flush any data

linux/hci/socket/socket.go

@@ -104,6 +104,15 @@ func open(fd, id int) (*Socket, error) {
 	if err := unix.Bind(fd, &sa); err != nil {
 		return nil, errors.Wrap(err, "can't bind socket to hci user channel")
 	}
+
+	// poll for 20ms to see if any data becomes available, then clear it
+	pfds := []unix.PollFd{unix.PollFd{Fd: int32(fd), Events: unix.POLLIN}}
+	unix.Poll(pfds, 20)
+	if pfds[0].Revents&unix.POLLIN > 0 {
+		b := make([]byte, 100)
+		unix.Read(fd, b)
+	}
+
 	return &Socket{fd: fd}, nil
 }