net: don't clear IFF_XMIT_DST_RELEASE in ether_setup

d88733150 introduced the IFF_SKB_TX_SHARING flag, which I unilaterally set in
ether_setup.  In doing this I didn't realize that other flags (such as
IFF_XMIT_DST_RELEASE) might be set prior to calling the ether_setup routine.
This patch changes ether_setup to or in SKB_TX_SHARING so as not to
inadvertently clear other existing flags.  Thanks to Pekka Riikonen for pointing
out my error

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Pekka Riikonen <priikone@iki.fi>
CC: "David S. Miller" <davem@davemloft.net>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethernet/eth.c

@@ -340,7 +340,7 @@ void ether_setup(struct net_device *dev)
 	dev->addr_len		= ETH_ALEN;
 	dev->tx_queue_len	= 1000;	/* Ethernet wants good queues */
 	dev->flags		= IFF_BROADCAST|IFF_MULTICAST;
-	dev->priv_flags		= IFF_TX_SKB_SHARING;
+	dev->priv_flags		|= IFF_TX_SKB_SHARING;
 
 	memset(dev->broadcast, 0xFF, ETH_ALEN);