generic: ar8216: fix unknown packet flooding for ar8229/ar8236

generic: ar8216: fix unknown packet flooding for ar8229/ar8236

ar8229 and ar8236 don't allow unknown unicast/multicast frames and
broadcast frames to be flooded to cpu port. This isn't desired behavior
for swconfig as we treat it as a standalone switch.
Current code doesn't enable unicast frame flooding for ar8229 and uses
wrong setup for ar8236. This commit fixes both of them by enabling port
0 flooding for all unknown frames.

Fixes: FS#2848
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
(cherry picked from commit 47f17b066259589b4a7b4181522321abf0660e18)