dpif-netdev: Use hmap instead of list+array for tracking ports.

dpif-netdev: Use hmap instead of list+array for tracking ports.

The goal is to make it easy to divide the ports into groups for handling
by threads.  It seems easy enough to do that by hash value, and a little
harder otherwise.

This commit has the side effect of raising the maximum number of ports from
256 to UINT32_MAX-1.  That is why some tests need to be updated:
previously, internally generated port names like "ovs_vxlan_4341" were
ignored because 4341 is bigger than the previous limit of 256.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>