core: raise the RLIMIT_NOFILE hard limit for all services by default

core: raise the RLIMIT_NOFILE hard limit for all services by default

Following the discussions with the kernel folks, let's substantially
increase the hard limit (but not the soft limit) of RLIMIT_NOFILE to
256K for all services we start.

Note that PID 1 itself bumps the limit even further, to the max the
kernel allows. We can deal with that after all.