[PATCH v3 2/3] nsproxy: attach to namespaces via pidfds

[Eric W. Biederman]

I am not thrilled about treating nstype as a flags fields when it is not
currently.  It was my hope when I designed the interface that not
treating nstype as a flags field would save us from the problem of bits
running out.

That aside.  It would be very good if the default version of setting
everything from a pidfd would set the root directory from the process it
is copying everything else from.

Eric