[$] The netfslib helper library

A new helper library for network filesystems, called netfslib, was the subjectof a filesystem session at the2022 Linux Storage,Filesystem, Memory-management and BPF Summit (LSFMM). David Howellsdevelopednetfslib, which was merged for 5.13 a year ago, and led the session.Some filesystems, like AFS and Ceph, are already using some of the servicesthat netfslib provides, while others are starting to look into it.