Fix readdir_with_callback() after cookies removal.
Fix readdir_with_callback() after cookies removal.

The non-cookie path was probably always broken and never used.

The file descriptor offset was never updated after a read so glibc and
other syscall consumers would end-up in an infinite loop.

Tested with the syscalls regression suite from IBM and with opera.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars