ofproto: Enable in-place modification for recirc actions.

ofproto: Enable in-place modification for recirc actions.

When modifying an existing datapath flow with recirculation actions,
the references to old (if any) recirculation actions need to be freed,
and references to new recirculation actions need to be stored.

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Ben Pfaff <blp@ovn.org>