NFSv2: EOF incorrectly set on short read

In cases where the server returns fewer bytes then those requested, we
can incorrectly set the eof flag for the file. Fixing this allows the
request to be retried with updated offset and count arguments.

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>