nfp: fix flower offload metadata flag usage

Hardware has no notion of new or last mask id, instead it makes use of the
message type (i.e. add flow or del flow) in combination with a single bit
in metadata flags to determine when to add or delete a mask id. Previously
we made use of the new or last flags to indicate that a new mask should be
allocated or deallocated, respectively. This incorrect behaviour is fixed
by making use single bit in metadata flags to indicate mask allocation or
deallocation.

Fixes: 43f84b72 ("nfp: add metadata to each flow offload")
Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>