dpif-netdev: preserve packet metadata fields across recirculation

If the actions executed during recirculation changed metadata fields,
then any actions after the recirculation returns would see those new
values. Now, all metadata are saved and restored across a recirculation.

Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
dpif-netdev: Use existing flow for computing dp hash

Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>