ofproto-dpif: Add idle_timeout parameter to ofproto_dpif_add_internal_flow()
This is in preparation for using the same helper as part of support
for using recirculation in conjunction series of actions including
with MPLS actions that are currently not able to be translated.
In that scenario the idle timeout will be used to expire internal
rules that are added to handle recirculation.
Signed-off-by: Simon Horman <horms@verge.net.au> Signed-off-by: Ben Pfaff <blp@nicira.com>