BUG/MINOR: init: only keep rlim_fd_cur if max is unlimited

BUG/MINOR: init: only keep rlim_fd_cur if max is unlimited

On some operating systems, RLIM_INFINITY is set to -1 so that when the
hard limit on the number of FDs is set to unlimited, taking the MAX
of both values keeps rlim_fd_cur and everything works. But on other
systems this values is defined as the highest positive integer. This
is what was observed on a 32-bit AIX 5.1. The effect is that maxsock
becomes 2^31-1 and that fdtab allocation fails.

Note that a simple workaround consists in manually setting maxconn in
the global section.

Let's ignore unlimited as soon as we retrieve rlim_fd_max so that all
systems behave consistently.

This may be backported as far as 2.0, though it doesn't seem like it
has annoyed anyone.