RDMA/cxgb3: Flush the receive queue when closing

- for kernel mode cqs, call event notification handler when flushing.
- flush QP when moving from RTS -> CLOSING.
- fix logic to identify a kernel mode qp.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>