dpif-netdev: Share emc and fast path output batches.

dpif-netdev: Share emc and fast path output batches.

Until now the exact match cache processing was able to handle only four
megaflows.  The rest of the packets was passed to the megaflow
classifier.

The limit was arbitraly set to four also because the algorithm used to
group packets in output batches didn't perform well with a lot of
megaflows.

After changing the algorithm and after some performance testing it seems
much better just to share the same output batches between the exact
match cache and the megaflow classifier.

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>