nfp: flower: do not assume mac/mpls matches

Remove the matching of mac/mpls as a default selection. These are not
necessarily set by a TC rule (unlike the port). Previously a mac/mpls
field would exist in every match and be masked out if not used. This patch
has no impact on functionality but removes unnessary memory assignment in
the match cmsg.

Signed-off-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>