mlxsw: spectrum_switchdev: Add support for getting and putting MDB entry

mlxsw: spectrum_switchdev: Add support for getting and putting MDB entry

A previous patch added support for init() and fini() for MDB entries. MDB
entry can be updated, ports can be added and removed from the entry. Add
get() and put() functions, the first one checks if the entry already exists
and otherwise initializes the entry. The second removes the entry just in
case that there are no more ports in this entry.

Use the list of the ports which was added in a previous patch. When the
list contains only one port which is not multicast router, and this port
is removed, the MDB entry can be removed. Use
'struct mlxsw_sp_mdb_entry.ports_count' to know how many ports use the
entry, regardless the use of multicast router ports.

When mlxsw_sp_mc_mdb_entry_put() is called with specific port which
supposed to be removed, check if the removal will cause a deletion of
the entry. If this is the case, call mlxsw_sp_mc_mdb_entry_fini() which
first deletes the MDB entry and then releases the PGT entry, to avoid a
temporary situation in which the MDB entry points to an empty PGT entry,
as otherwise packets will be temporarily dropped instead of being flooded.

The new functions will be used in the next patches.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>