ks8851: Fix interpretation of rxlen field.

According to the Datasheet (page 52):
15-12 Reserved
11-0 RXBC Receive Byte Count
This field indicates the present received frame byte size.

The code has a bug:
                 rxh = ks8851_rdreg32(ks, KS_RXFHSR);
                 rxstat = rxh & 0xffff;
                 rxlen = rxh >> 16; // BUG!!! 0xFFF mask should be applied

Signed-off-by: Max Nekludov <Max.Nekludov@us.elster.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/micrel/ks8851.c

@@ -528,7 +528,7 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
 	for (; rxfc != 0; rxfc--) {
 		rxh = ks8851_rdreg32(ks, KS_RXFHSR);
 		rxstat = rxh & 0xffff;
-		rxlen = rxh >> 16;
+		rxlen = (rxh >> 16) & 0xfff;
 
 		netif_dbg(ks, rx_status, ks->netdev,
 			  "rx: stat 0x%04x, len 0x%04x\n", rxstat, rxlen);