Open the TUN or TAP device.

def open(self):
        """Open the TUN or TAP device."""
        if not self.closed:
            return
        self.outs = self.ins = open(
            "/dev/net/tun" if LINUX else ("/dev/%s" % self.iface), "r+b",
            buffering=0
        )
        if LINUX:
            from fcntl import ioctl
            # TUNSETIFF = 0x400454ca
            # IFF_TUN = 0x0001
            # IFF_TAP = 0x0002
            # IFF_NO_PI = 0x1000
            ioctl(self.ins, 0x400454ca, struct.pack(
                "16sH", bytes_encode(self.iface),
                0x0001 if self.mode_tun else 0x1002,
            ))
        self.closed = False