Fix FC target mode in mpt(4), broken in multiple ways.

• Not set BufferLength caused receive of empty ATIOs.
• CDB length guessing was broken at least for RC16.
• mpt_req_untimeout() was called with wrong req parameter.
• Sense data reporting was broken in several ways.

With this change my LSI7204EP-LC can pass at least basic tests as target.
The code is still far from perfect, but finally I found second hw/driver
after isp(4) that really can work in CAM target mode.

MFC after: 2 weeks