Fixes <https://issues.guix.info/39670>.
Combined with commit def6e2ae46, this allows unprivileged users to mount file
systems marked with the "user" option. It adds less than 4 MiB to the closure
of the lightweight-desktop.tmpl operating system template.
* gnu/services/desktop.scm (%desktop-services): Extend the
setuid-program-service-type service with the 'mount.nfs' and 'mount.nfs-3g'
programs.
Reported-by: Nathan Dehnel <ncdehnel@gmail.com>