The _aa_dirat_for_each() function used the DIR * type for its first
parameter. It then switched back and forth between the directory file
descriptors, retrieved with dirfd(), and directory streams, retrieved
with fdopendir(), when making syscalls and calling the call back
function.

This patch greatly simplifies the function by simply using directory
file descriptors. No functionality is lost since callers can still
easily use the function after calling dirfd() to retrieve the underlying
file descriptor.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>