nfp: flower: offload list of IPv6 tunnel endpoint addresses

Fw requires a list of IPv6 addresses that are used as tunnel endpoints to
enable correct decap of tunneled packets.

Store a list of IPv6 endpoints used in rules with a ref counter to track
how many times it is in use. Offload the entire list any time a new IPv6
address is added or when an address is removed (ref count is 0).

Signed-off-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>