raising openfiles-cur above the implicit -max value (1024 on at least the
common arch) results in the setting not being applied at all.
Earlier version OK tom@ danj@ ajacoutot@ benno@ krw@ beck@, suggestion about
openfiles= from millert@ - changes in this version are to use 1024 for -max
rather than 512 to avoid changing the existing hard limit, and just use
openfiles= for bgpd/unbound where max and cur are the same value.