ofproto: Don't count hidden rules in table stats.

ofproto: Don't count hidden rules in table stats.

The hidden rules created by in-band control and fail-open should not be
included in the table stats reported via OpenFlow.  I seem to recall that
this was done correctly in some previous version but it has broken since
then.  This commit fixes the problem and adds a test that should make it
harder to break again in the future.

Reported-by: Ashok Chippa <a.n.chippa@gmail.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>