Don't use error categories as if they were actually errors.

Don't use error categories as if they were actually errors.

The OFPERR_* naming scheme is confusing, because it mixes categories with
specific errors.  Categories can't be encoded for sending to controllers,
so this is a problem.  This commit fixes up the cases where categories
were used as errors, replacing them by real errors types.

Signed-off-by: Jarno Rajahalme <jarno.rajahalme@nsn.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>