mlxsw: spectrum_span: Rename function

Next patch will introduce mlxsw_sp_span_port_buffer_disable() function
that disables the egress buffer on an analyzed port. Rename the opposite
function that updates the buffer on an analyzed port accordingly.

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