rdma: validate RDMAControlHeader::len

RMDAControlHeader::len is provided from remote, so validate it.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Reviewed-by: Michael R. Hines <mrhines@us.ibm.com>
Signed-off-by: Isaku Yamahata <yamahata@private.email.ne.jp>
Signed-off-by: Michael R. Hines <mrhines@us.ibm.com>
Message-id: 1376078746-24948-3-git-send-email-mrhines@linux.vnet.ibm.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
