Add support for allocating and freeing KVD entries for IPv6 addresses.

These addresses are programmed by the RIPS register and referenced by
the RATR and RTDP registers for IPv6 underlay encapsulation and
decapsulation, respectively.
Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>