dpif-netdev: Clear flow batches before execute.

dpif-netdev: Clear flow batches before execute.

When executing actions, it's possible a recirculation will occur
causing dp_netdev_input() to be called multiple times.  If the batch
pointers embedded in dp_netdev_flow aren't cleared, it's possible
packets after the recirculation will be reinserted into a batch
associated with the original lookup.  This could be very bad.

This patch fixes the problem by zeroing out flow batch pointers before
calling packet_batch_execute().  This probably has a slightly negative
performance impact, though I haven't tried it.

Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Daniele Di Proietto <diproiettod@vmware.com>