Track the highest priority flow in each specific flowtable.

During match on key, if priority of the flow entry previously found is
greater than all flows in a given specific flowtable, then skip hashing into
the specific flowtable.
Addressed review comments.
max_priority -> cur_priority.
Merge into master from pull request #22:
Track the highest priority flow in each specific flowtable. (https://github.com/floodlight/ivs/pull/22)