nfsd: make a copy of struct iattr before calling notify_change
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2207969
notify_change can modify the iattr structure. In particular it can end up setting ATTR_MODE when ATTR_KILL_SUID is already set, causing a BUG() if the same iattr is passed to notify_change more than once.
Make a copy of the struct iattr before calling notify_change.
Signed-off-by: Jeffrey Layton jlayton@redhat.com