IB/qib: Remove qib_post_receive and use rdmavt version

This patch removes the simple post recv function in favor of using rdmavt.
The packet receive processing still lives in the driver though.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Harish Chegondi <harish.chegondi@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>