mlxsw: spectrum: Add a new type of KVD linear record

When the device needs to flood an overlay packet to remote VTEPs it
retrieves a pointer to the head of a linked-list of records that store
the IP addresses of these VTEPs.

These records are stored in the KVD linear memory and configured via the
Tunneling NVE Underlay Multicast Table (TNUMT) register.

Add a new KVD linear entry type for these records, so that we will be
able to allocate and free them.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>