upcall: Revalidate using cache of mask, actions.

upcall: Revalidate using cache of mask, actions.

This allows us to ignore most fields of a flow_dump, requiring only the
flow key for looking up the ukey. Fetching flows can also be avoided in
the corner case where a flow is missed from a dump but revalidation is
required.

A future patch will modify the datapath interface to allow datapaths to
skip dumping these fields, so this cache will be used instead.

Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>