match: Do not skip formatting a zero dp_hash.

match: Do not skip formatting a zero dp_hash.

The dp_hash match should be printed whenever it is being matched.  We
keep the old behavior for flow_format(), which is mostly used to
format PACKET_IN messages. This keeps those messages tidier and avoids
changing a lot of test cases.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Andy Zhou <azhou@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>