ofproto-dpif: Pull xlate_actions() into its own file.

ofproto-dpif: Pull xlate_actions() into its own file.

Ideally, this patch would move xlate_actions() into it's own module
with a clearly defined regular interface which is minimally
dependent on ofproto-dpif.  While, I've done this in a prototype,
moving large amounts of code into a new file while simultaneously
changing the logic and keeping up with changes to master has proved
nearly impossible.

This patch takes a different approach.  It simply copies the logic
directly from ofproto-dpif with no changes.  Once this is in,
future patches can begin breaking the ties between
ofproto-dpif-xlate and ofproto-dpif proper.

Signed-off-by: Ethan Jackson <ethan@nicira.com>