Use -inet6 flag for BSD route where needed

[gmacon]

My company started providing IPv6 addresses, and I got this error on macOS:

route: bad address: xxxx:xxx:xxx:xxxx::xxx
Traceback (most recent call last):
  File "/usr/local/bin/vpn-slice", line 11, in <module>
    load_entry_point('vpn-slice', 'console_scripts', 'vpn-slice')()
  File "vpn-slice/vpn_slice/__main__.py", line 462, in main
    do_connect(env, args)
  File "vpn-slice/vpn_slice/__main__.py", line 171, in do_connect
    providers.route.replace_route(dest, dev=env.tundev)
  File "vpn-slice/vpn_slice/mac.py", line 51, in add_route
    self._route(*args)
  File "vpn-slice/vpn_slice/mac.py", line 38, in _route
    return subprocess.check_output([self.route, '-n'] + list(map(str, args)), universal_newlines=True)
  File "python3.7/subprocess.py", line 411, in check_output
    **kwargs).stdout
  File "python3.7/subprocess.py", line 512, in run
    output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['/sbin/route', '-n', 'add', '-interface', 'xxxx:xxx:xxx:xxxx::xxx', 'utun1']' returned non-zero exit status 68.

This PR adds the -inet6 flag that BSD route expects in this case.

[dlenski]

Perhaps we can make this a bit less verbose on the Python side, and a bit more explicit on the route side, by using something like this instead?

args = ['add', ('-inet6' if destination.version == 6 else '-inet')]

[gmacon]

Sure. I'll make that modification.

[dlenski]

👍 👍 👍

[gmacon]

Thanks for the quick response!