recoco: Fixes to scheduling priorities

Peter Peresini pointed out that the check for t >= 1 was
nonsense.  It was *supposed* to be an early-out for
priority==1, which it now is.

In the process of fixing that, I noticed that it looked
like the priority check was backwards and like a slightly
different check on the ready list would also make sense.
openflow: Better defaults for queue_stats_request

The port and queue to be queried used to default to 0, but
are now the more sensible "ALL" values.
openflow.nicira: header_only pack for nxm_entries

It use useful in some cases to be able to pack only the
header of an nxm_entry.  This is now supported.

This also fixes a bug that kept nx_reg_load actions
from working.

Thanks to Saul St. John for pointing out the issue.
openflow.nicira: Fix _eq in nx_reg_load

This was doing a bad job for checking equality of
nx_reg_load actions.