nfp: flower: free dst_entry in route table

We need to release the refcnt on dst_entry in the route table, otherwise
we will leak the route.

Fixes: 8e6a9046 ("nfp: flower vxlan neighbour offload")
Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Signed-off-by: Louis Peens <louis.peens@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>