craa_type_mask is bitmap4 per RFC5661. We need to expect a length before
extracting bitmap value.

Cc: Alexandros Batsakis <batsakis@netapp.com>
Signed-off-by: NPeng Tao <peng_tao@emc.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>