[NETPOLL]: Revert two bogus cleanups that broke netconsole.

Based upon a report by Andrew Morton and code analysis done
by Jarek Poplawski.

This reverts 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7 ("[NETPOLL]:
Kill NETPOLL_RX_DROP, set but never tested.")  and
c7b6ea24b43afb5749cb704e143df19d70e23dea ("[NETPOLL]: Don't need
rx_flags.").

The rx_flags did get tested for zero vs. non-zero and therefore we do
need those tests and that code which sets NETPOLL_RX_DROP et al.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index a0525a1..e3d7959 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -25,6 +25,7 @@
 
 struct netpoll_info {
 	atomic_t refcnt;
+	int rx_flags;
 	spinlock_t rx_lock;
 	struct netpoll *rx_np; /* netpoll that registered an rx_hook */
 	struct sk_buff_head arp_tx; /* list of arp requests to reply to */
@@ -50,12 +51,12 @@
 	unsigned long flags;
 	int ret = 0;
 
-	if (!npinfo || !npinfo->rx_np)
+	if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
 		return 0;
 
 	spin_lock_irqsave(&npinfo->rx_lock, flags);
-	/* check rx_np again with the lock held */
-	if (npinfo->rx_np && __netpoll_rx(skb))
+	/* check rx_flags again with the lock held */
+	if (npinfo->rx_flags && __netpoll_rx(skb))
 		ret = 1;
 	spin_unlock_irqrestore(&npinfo->rx_lock, flags);