ofp-util: Fix table features decoding of action and instruction fields.

Parsing of actions was wrong because OF1.3 says that non-experimenter
actions are 4 bytes and don't include padding.  This fixes the problem.

Parsing of instructions seems wrong too because OF1.3 says that
non-experimenter instructions are 4 bytes (though it is not explicit about
padding as it is for actions).  This fixes the problem there too.

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