We ignored errors for simple syntax in `PortOpt` (missed that in the
previous migration of this code). This make sure we don't ignore
`nat.Parse` errors.
Test has been migrate too (errors are not exactly the same as before
though -_-)
Signed-off-by: Vincent Demeester <vincent@sbr.pm>
Upstream-commit: 6f8f1d20a2
Component: cli