ofproto-dpif-upcall: Use flow_wildcards_has_extra().
Update the comment in ukey_revalidate() to reflect the fact that the
mask in ukey is not the datapath mask, but the originally translated
flow wildcards.
Use flow_wildcards_has_extra() instead of open coding equivalent (but
different) functionality. The old form and the code in
flow_wildcards_has_extra() ((dp | wc != dp) and (dp & wc != wc),
respecively) give the same result: