mlxsw: spectrum_span: Add APIs to get / put an analyzed port

mlxsw: spectrum_span: Add APIs to get / put an analyzed port

An analyzed port is a port whose incoming / outgoing traffic is mirrored
to a SPAN agent and analyzed on a remote server.

A port can be analyzed by multiple tc filters and therefore the
corresponding analyzed port entry needs to be reference counted. This is
significant because ports whose outgoing traffic is analyzed need to
have an egress mirror buffer.

Add APIs to get / put an analyzed port. Allocate an egress mirror buffer
on a port when it is first inspected at egress and free the buffer when
it is no longer inspected at egress.

Protect the list of analyzed ports with a mutex, as a later patch will
traverse it from a context in which RTNL lock is not held.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>