main: bump up RLIMIT_NOFILE for systemd itself

main: bump up RLIMIT_NOFILE for systemd itself

For setups with many listening sockets the default kernel resource limit
of 1024 fds is not enough. Bump this up to 64K to avoid any limitations
in this regard. We are careful to pass on the kernel default to daemons
however, since normally resource limits are a good to enforce,
especially since select() can't handle fds > 1023.