openvswitch: Fix ovs_flow_free() ovs-lock assert.

ovs_flow_free() is not called under ovs-lock during packet
execute path (ovs_packet_cmd_execute()). Since packet execute
does not touch flow->mask, there is no need to take that
lock either. So move assert in case where flow->mask is checked.

Found by code inspection.
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>

net/openvswitch/flow_table.c

@@ -158,11 +158,13 @@ void ovs_flow_free(struct sw_flow *flow, bool deferred)
 	if (!flow)
 		return;
 
-	ASSERT_OVSL();
-
 	if (flow->mask) {
 		struct sw_flow_mask *mask = flow->mask;
 
+		/* ovs-lock is required to protect mask-refcount and
+		 * mask list.
+		 */
+		ASSERT_OVSL();
 		BUG_ON(!mask->ref_count);
 		mask->ref_count--;