Crash when using --nat ext:IP:Port syntax

[palango]

Problem Definition

When using the --nat=ext:10.0.2.3:40001 syntax the client crashes.

$ raiden--nat=ext:10.0.2.3:40001
Traceback (most recent call last):
  File "/Users/paul/Work/raiden-p3/bin/raiden", line 11, in <module>
    load_entry_point('raiden', 'console_scripts', 'raiden')()
  File "/Users/paul/Work/raiden/raiden/__main__.py", line 11, in main
    run(auto_envvar_prefix='RAIDEN')
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 696, in main
    with self.make_context(prog_name, args, **extra) as ctx:
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 621, in make_context
    self.parse_args(ctx, args)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 1018, in parse_args
    rest = Command.parse_args(self, ctx, args)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 880, in parse_args
    value, args = param.handle_parse_result(ctx, opts, args)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 1396, in handle_parse_result
    value = self.full_process_value(ctx, value)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 1681, in full_process_value
    return Parameter.full_process_value(self, ctx, value)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 1365, in full_process_value
    value = self.process_value(ctx, value)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 1355, in process_value
    return self.type_cast_value(ctx, value)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 1344, in type_cast_value
    return _convert(value, (self.nargs != 1) + bool(self.multiple))
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/core.py", line 1342, in _convert
    return self.type(value, self, ctx)
  File "/Users/paul/Work/raiden-p3/lib/python3.6/site-packages/click/types.py", line 38, in __call__
    return self.convert(value, param, ctx)
  File "/Users/paul/Work/raiden/raiden/ui/cli.py", line 261, in convert
    IPv4Address(ip.decode('UTF-8', 'ignore'))
AttributeError: 'str' object has no attribute 'decode'

System Description

Darwin yoda 17.4.0 Darwin Kernel Version 17.4.0: Sun Dec 17 09:19:54 PST 2017; root:xnu-4570.41.2~1/RELEASE_X86_64 x86_64
/usr/local/bin/solc
solc, the solidity compiler commandline interface
Version: 0.4.20+commit.3155dd80.Darwin.appleclang
/usr/local/bin/geth
Geth
Version: 1.8.1-stable
Architecture: amd64
Protocol Versions: [63 62]
Network Id: 1
Go Version: go1.10
Operating System: darwin
GOPATH=
GOROOT=/usr/local/opt/go/libexec
/Users/paul/Work/raiden-p3/bin/raiden
{
  "raiden": "0.2.0+git.r7c8ced6f",
  "python_implementation": "CPython",
  "python_version": "3.6.4",
  "system": "macOS 10.13.3 64bit"
}
9c11d2d2b3569a92c21c9e6a77f80fe9a986a15b