ofproto: Shrink struct rule_actions slightly.

ofproto: Shrink struct rule_actions slightly.

Nothing actually used 'provider_meter_id', but some code did want to know
whether there was a meter, so we can save a little space by using a bool
instead.  An upcoming commit will add a second bool member.  This change
allows that bool to be added without using extra space.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>