Client sends a SETATTR request after OPEN for updating attributes.
For create file with S_ISGID is set, the S_ISGID in SETATTR will be
ignored at nfs server as chmod of no PERMISSION.

v3, same as v2.
Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>