net: xilinx: axienet: Support IFF_ALLMULTI

Add support for IFF_ALLMULTI by configuring a single filter to match the
multicast address bit. This allows us to keep promiscuous mode disabled,
even when we have more than four multicast addresses. An even better
solution would be to "pack" addresses into the available CAM registers,
but that can wait for a future series.

Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240822154059.1066595-6-sean.anderson@linux.dev


Signed-off-by: Jakub Kicinski <kuba@kernel.org>