RDMA/iser: don't send an rkey if all data is written as immadiate-data

We might get some bogus error completions in case the target will
remotely invalidate the rkey and the HCA will need to retransmit
from this buffer.
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/ulp/iser/iser_initiator.c

@@ -137,8 +137,10 @@ iser_prepare_write_cmd(struct iscsi_task *task,
 
 	if (unsol_sz < edtl) {
 		hdr->flags     |= ISER_WSV;
+		if (buf_out->data_len > imm_sz) {
 			hdr->write_stag = cpu_to_be32(mem_reg->rkey);
 			hdr->write_va = cpu_to_be64(mem_reg->sge.addr + unsol_sz);
+		}
 
 		iser_dbg("Cmd itt:%d, WRITE tags, RKEY:%#.4X "
 			 "VA:%#llX + unsol:%d\n",