Commit 9a3edc8 modified the behaviour of ZFS's
VOP_READDIR() such that it will reply EINVAL for
an offset past EOF on the directory.
This exposed a latent bug in the NFSv4 Readdir
code, which would attempt a Readdir with an
offset beyond EOF for a directory that consists
of only "." and "..". This happened because NFSv4
does not reply "." or ".." to the client and, after
skipping over them, attempted another VOP_READDIR().
This patch fixes the problem by checking the eofflag
for the case where all entries have been skipped over.