OFStateManager: remove use of flow_add from flow stats handler

Instead use the flowtable entry fields to populate the of_flow_stats_entry.

I also noticed the flags field is missing from the LOXI of_flow_stats_entry
class (replaced by padding). I'll fix that separately.
OFStateManager: remove use of flow_add from flow removal

Instead use the flowtable entry fields to populate the of_flow_removed.

Also populated the table_id field which was added in OpenFlow 1.1.
OFStateManager: remove flow_add from flowtable entry

This saves about 18% RSS for an IVS with a full flowtable.
OFStateManager: fix ft_entry_t comment referring to flow_add
OFStateManager: fix compile error in send_flow_removed_message
Merge into master from pull request #32:
Remove flow-add from OFStateManager flowtable entry (https://github.com/floodlight/indigo/pull/32)