svcrdma: Clean up allocation of svc_rdma_recv_ctxt

The physical device's favored NUMA node ID is available when
allocating a recv_ctxt. Use that value instead of relying on the
assumption that the memory allocation happens to be running on a
node close to the device.

This clean up eliminates the hack of destroying recv_ctxts that
were not created by the receive CQ thread -- recv_ctxts are now
always allocated on a "good" node.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>