When reading kuids from the wire map them into the initial user
namespace, and validate the mapping succeded.

When reading kgids from the wire map them into the initial user
namespace, and validate the mapping succeded.

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