net: fix network drivers ndo_start_xmit() return values

Fix up remaining drivers returning a magic or an errno value from their
ndo_start_xmit() functions that were missed in the first pass:

- isdn_net: missed conversion
- bpqether: missed conversion: skb is freed, so return NETDEV_TX_OK
- hp100: intention appears to be to resubmit skb once resources are
  available, but due to no queue handling it is dropped for now.
- lapbether: skb is freed, so return NETDEV_TX_OK

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/hamradio/bpqether.c b/drivers/net/hamradio/bpqether.c
index 5105548..abcd19a 100644
--- a/drivers/net/hamradio/bpqether.c
+++ b/drivers/net/hamradio/bpqether.c
@@ -260,7 +260,7 @@
 	 */
 	if (!netif_running(dev)) {
 		kfree_skb(skb);
-		return -ENODEV;
+		return NETDEV_TX_OK;
 	}
 
 	skb_pull(skb, 1);