BUG/MINOR: init: never lower rlim_fd_max

BUG/MINOR: init: never lower rlim_fd_max

If a ulimit-n value is set, we must not lower the rlim_max value if the
new value is lower, we must only adjust the rlim_cur one. The effect is
that on very low values, this could prevent a master-worker reload, or
make an external check fail by lack of FDs.

This may be backported to 1.9 and earlier, but it depends on this patch
"MINOR: global: keep a copy of the initial rlim_fd_cur and rlim_fd_max
values".