IB/rxe: avoid double kfree_skb

When skb is sent, it will pass the following functions in soft roce.

rxe_send [rdma_rxe]
    ip_local_out
        __ip_local_out
        ip_output
            ip_finish_output
                ip_finish_output2
                    dev_queue_xmit
                        __dev_queue_xmit
                            dev_hard_start_xmit

In the above functions, if error occurs in the above functions or
iptables rules drop skb after ip_local_out, kfree_skb will be called.
So it is not necessary to call kfree_skb in soft roce module again.
Or else crash will occur.

The steps to reproduce:

     server                       client
    ---------                    ---------
    |1.1.1.1|<----rxe-channel--->|1.1.1.2|
    ---------                    ---------

On server: rping -s -a 1.1.1.1 -v -C 10000 -S 512
On client: rping -c -a 1.1.1.1 -v -C 10000 -S 512

The kernel configs CONFIG_DEBUG_KMEMLEAK and
CONFIG_DEBUG_OBJECTS are enabled on both server and client.

When rping runs, run the following command in server:

iptables -I OUTPUT -p udp  --dport 4791 -j DROP

Without this patch, crash will occur.

CC: Srinivas Eeda <srinivas.eeda@oracle.com>
CC: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/sw/rxe/rxe_req.c

@@ -728,7 +728,6 @@ next_wqe:
 		rollback_state(wqe, qp, &rollback_wqe, rollback_psn);
 
 		if (ret == -EAGAIN) {
-			kfree_skb(skb);
 			rxe_run_task(&qp->req.task, 1);
 			goto exit;
 		}

drivers/infiniband/sw/rxe/rxe_resp.c

@@ -742,7 +742,6 @@ static enum resp_states read_reply(struct rxe_qp *qp,
 	err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
 	if (err) {
 		pr_err("Failed sending RDMA reply.\n");
-		kfree_skb(skb);
 		return RESPST_ERR_RNR;
 	}
 
@@ -954,10 +953,8 @@ static int send_ack(struct rxe_qp *qp, struct rxe_pkt_info *pkt,
 	}
 
 	err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
-	if (err) {
+	if (err)
 		pr_err_ratelimited("Failed sending ack\n");
-		kfree_skb(skb);
-	}
 
 err1:
 	return err;
@@ -1141,7 +1138,6 @@ static enum resp_states duplicate_request(struct rxe_qp *qp,
 			if (rc) {
 				pr_err("Failed resending result. This flow is not handled - skb ignored\n");
 				rxe_drop_ref(qp);
-				kfree_skb(skb_copy);
 				rc = RESPST_CLEANUP;
 				goto out;
 			}