datapath: Drop port information from odp_stats.

datapath: Drop port information from odp_stats.

As with n_flows, n_ports was used regularly by userspace to determine how
much memory to allocate when listing ports, but it is no longer needed for
that.  max_ports, on the other hand, is necessary but it is also a fixed
value for the kernel datapath right now and if we expand it we can also
come up with a way to report the expanded value.

The remaining members of odp_stats are actually real statistics that I
intend to keep.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>