ofproto-dpif: Make it easier to credit statistics for resubmits.

ofproto-dpif: Make it easier to credit statistics for resubmits.

Until now, crediting statistics to OpenFlow rules due to "resubmit" actions
has required setting up a "resubmit hook" with a callback function and
auxiliary data.  This commit makes it easier to do, by adding a member to
struct action_xlate_ctx that specifies statistics to credit to each
resubmitted rule.

This commit includes one small behavioral change as an optimization.
Previously, rule_execute() translated the rule twice: once to get the ODP
actions, then a second time after executing the ODP actions to credit
statistics to the rules.  After this commit, rule_execute() translates the
rule only once, crediting statistics as a side effect.  The difference only
becomes visible when executing the actions fails: previously the statistics
would not be incremented, after this commit they will be.  It is very
unusual for executing actions to fail (generally this indicates a bug) so
I'm not concerned about it.

Signed-off-by: Ben Pfaff <blp@nicira.com>