IB/rxe: fix for duplicate request processing and ack psns

IB/rxe: fix for duplicate request processing and ack psns

Don't reset the resp opcode for a replayed read response.
The resp opcode could be in the middle of a write or send
sequence, when the duplicate read request was received.
An example sequence is as follows:
- Receive read request for 12KB PSN 20. Transmit read response
  first, middle and last with PSNs 20,21,22.
- Receive write first PSN 23.
  At this point the resp psn is 24 and resp opcode is write first.
- The sender notices that PSN 20 is dropped and retransmits.
  Receive read request for 12KB PSN 20. Transmit read response
  first, middle and last with PSNs 20,21,22. The resp opcode is
  set to -1, the resp psn remains 24.
- Receive write first PSN 23. This is processed by duplicate_request().
  The resp opcode remains -1 and resp psn remains 24.
- Receive write middle PSN 24. check_op_seq() reports a missing
  first error since the resp opcode is -1.

When sending an ack for a duplicate send or write request,
use the psn of the previous ack sent. Do not use the psn
of a read response for the ack.
An example sequence is as follows:
- Receive write PSN 30. Transmit ACK for PSN 30.
- Receive read request 4KB PSN 31. Transmit read response with
  PSN 31. The resp psn is now 32.
- The sender notices that PSN 30 is dropped and retransmits.
  Receive write PSN 30. duplicate_request() sends an ACK with
  PSN 31. That is incorrect since PSN 31 was a read request.

Signed-off-by: Vijay Immanuel <vijayi@attalasystems.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>