When reading uids and gids off the wire convert them to
kuids and kgids.  If the conversion results in an invalid
result don't set the ATTR_UID or ATTR_GID.

When putting kuids and kgids onto the wire first convert
them to uids and gids the other side will understand.

Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>