xprtrdma: Split the completion queue

xprtrdma: Split the completion queue

The current CQ handler uses the ib_wc.opcode field to distinguish
between event types. However, the contents of that field are not
reliable if the completion status is not IB_WC_SUCCESS.

When an error completion occurs on a send event, the CQ handler
schedules a tasklet with something that is not a struct rpcrdma_rep.
This is never correct behavior, and sometimes it results in a panic.

To resolve this issue, split the completion queue into a send CQ and
a receive CQ. The send CQ handler now handles only struct rpcrdma_mw
wr_id's, and the receive CQ handler now handles only struct
rpcrdma_rep wr_id's.

Fix suggested by Shirley Ma <[email protected]>

Reported-by: Rafael Reiter <[email protected]>
Fixes: 5c635e09cec0feeeb310968e51dad01040244851
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=73211
Signed-off-by: Chuck Lever <[email protected]>
Tested-by: Klemens Senn <[email protected]>
Tested-by: Steve Wise <[email protected]>
Signed-off-by: Anna Schumaker <[email protected]>