datapaths: Don't include name in log messages

Since we're using a custom logger named after the switch, we
shouldn't have to include the name in the message itself.
datapaths: Reformat if statements

This brings them all into line with POX convention
datapaths: Fix bad string formats

All string format operator right-hand-sides are now tuples as they
should be.

Also, some integers were being formatted as hex when they are
probably better off as decimal -- fixed.
datapaths: Fix some buffer_id checks
datapaths: Allow table_id to be 0

flow/aggregate stats requests were requiring that the table specified
be TABLE_ALL, but 0 should also be allowed.
datapaths: First stab at table_stats

This is a first stab at supporting table_stats requests.