mkiss: ax_bump() locking fix

According to one of OOPSes reported by Jann softirq can break
while skb is prepared for netif_rx. The report isn't complete,
so the real reason of the later bug could be different, but
IMHO this locking break in ax_bump is unsafe and unnecessary.
Reported-and-tested-by: Jann Traschewski <jann@gmx.de>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/net/hamradio/mkiss.c

@@ -289,7 +289,6 @@ static void ax_bump(struct mkiss *ax)
 			*ax->rbuff &= ~0x20;
 		}
  	}
-	spin_unlock_bh(&ax->buflock);
 
 	count = ax->rcount;
 
@@ -297,17 +296,17 @@ static void ax_bump(struct mkiss *ax)
 		printk(KERN_ERR "mkiss: %s: memory squeeze, dropping packet.\n",
 		       ax->dev->name);
 		ax->stats.rx_dropped++;
+		spin_unlock_bh(&ax->buflock);
 		return;
 	}
 
-	spin_lock_bh(&ax->buflock);
 	memcpy(skb_put(skb,count), ax->rbuff, count);
-	spin_unlock_bh(&ax->buflock);
 	skb->protocol = ax25_type_trans(skb, ax->dev);
 	netif_rx(skb);
 	ax->dev->last_rx = jiffies;
 	ax->stats.rx_packets++;
 	ax->stats.rx_bytes += count;
+	spin_unlock_bh(&ax->buflock);
 }
 
 static void kiss_unesc(struct mkiss *ax, unsigned char s)