ofproto-dpif-xlate: Calculate 'ofpacts' in more restricted scope.

ofproto-dpif-xlate: Calculate 'ofpacts' in more restricted scope.

This moves the calculation of 'ofpacts' closer to its actual use, which
in my opinion makes the code easier to read.

This commit also expands the circumstances in which OVS omits sending
NetFlow records from those where there is exactly one OpenFlow action that
sends to controller, to those where any OpenFlow action sends to
controller.  I doubt that this is a big deal.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>