xprtrdma: Put rpcrdma_reps before waking the tear-down completion

Ensure the tear-down completion is awoken only /after/ we've stopped
fiddling with rpcrdma_rep objects in rpcrdma_post_recvs().

Fixes: 15788d1d

 ("xprtrdma: Do not refresh Receive Queue while it is draining")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>