tmpfiles: let's bump RLIMIT_NOFILE for tmpfiles

tmpfiles: let's bump RLIMIT_NOFILE for tmpfiles

We potentially might descent into quite deep directory trees. Let's
hence make sure we can allocate a lot of fds.

(This reflects the fact that glibc nftw() and friends have some logic in
place to reduce fd usage while descending into directory trees. Doing so
is a bit nasty I think, and given that fds are basically free now, if we
ask for them, lte's just protect ourselves and make use of that)

(No, I am not aware of a real-world case where this was necessary, but
let's better be safe than sorry)