The function lan966x_port_change_rx_flags() was used only when
IFF_PROMISC flag was set. In that case it was setting to copy all the
frames to the CPU instead of removing any RX filters. Therefore remove
it.

Fixes: d28d6d2e ("net: lan966x: add port module support")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>