nfp: flower: fixup ipv6/ipv4 route lookup for neigh events

When a callback is received to invalidate a neighbour entry
there is no need to try and populate any other flow information.
Only the flowX->daddr information is needed as lookup key to delete
an entry from the NFP neighbour table. Fix this by only doing the
lookup if the callback is for a new entry.

As part of this cleanup remove the setting of flow6.flowi6_proto, as
this is not needed either, it looks to be a possible leftover from a
previous implementation.

Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>