NTB: Rename Variables for NTB-RP

Many variable names in the NTB driver refer to the primary or secondary
side.  However, these variables will be used to access the reverse case
when in NTB-RP mode.  Make these names more generic in anticipation of
NTB-RP support.

Signed-off-by: Jon Mason <jon.mason@intel.com>
diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index ae86572..ae61b44 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -1216,7 +1216,7 @@
 	wmb();
 	iowrite32(entry->flags | DESC_DONE_FLAG, &hdr->flags);
 
-	ntb_ring_sdb(qp->ndev, qp->qp_num);
+	ntb_ring_doorbell(qp->ndev, qp->qp_num);
 
 	/* The entry length can only be zero if the packet is intended to be a
 	 * "link down" or similar.  Since no payload is being sent in these