ofp-util: Fix table features decoding of match and mask.

The call to parse_oxms() inside ofputil_decode_table_features() sets only
one bit in either 'match' or 'mask' for a given field that is matchable:
in 'mask' if the field is arbitrarily maskable or in 'match' otherwise.
The code at the end of ofputil_decode_table_features() mishandled this,
assuming that an arbitrarily matchable field would have that bit set in
both.  This meant that arbitrarily matchable fields were being
misinterpreted as not matchable at all.  This commit fixes the problem.

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