Add missing fields to the bandwidth_record table

I was double-checking the bandwidth-file-spec making sure we have every item mentioned there accounted for in our table. I think here are the missing ones that still need to get added:

rtt
relay_recent_measurement_failure_count
relay_recent_measurements_excluded_near_count
relay_recent_measurements_excluded_old_count
relay_recent_measurements_excluded_few_count
under_min_report
unmeasured
vote
xoff_recv
xoff_sent