openvswitch: Add skb_clone NULL check for the sampling action.

Fix a bug where skb_clone() NULL check is missing in sample action
implementation.
Signed-off-by: Andy Zhou <azhou@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>

net/openvswitch/actions.c

@@ -477,6 +477,8 @@ static int sample(struct datapath *dp, struct sk_buff *skb,
 		skb_get(skb);
 	} else {
 		sample_skb = skb_clone(skb, GFP_ATOMIC);
+		if (!sample_skb) /* Skip sample action when out of memory. */
+			return 0;
 	}
 
 	/* Note that do_execute_actions() never consumes skb.