ofproto: Send monitor updates if a flow mod changes a rules actions

Without this change a monitor update will be sent when a flow mod changes
a rules cookie but not if only the actions are updated. This appears
to be a logic error.

I noticed this while working on implementing OpenFlow1.4 flow monitor
as an OpenFlow1.4 flow mod does not update a rules cookie.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>