r8169: remove multicast filter limit

Once upon a time, when r8169 was new, the multicast filter limit code
was copied from RTL8139 driver. There the filter limit is even
user-configurable.
The filtering is hash-based and we don't have perfect filtering.
Actually the mc filtering on RTL8125 still seems to be the same
as used on 8390/NE2000. So it's not clear to me which benefit it
should bring when switching to all-multi mode once a certain number
of filter bits is set. More the opposite: Filtering out at least
some unwanted mc traffic is better than no filtering.
Also the available chip documentation doesn't mention any restriction.
Therefore remove the filter limit.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/57076c05-3730-40d1-ab9a-5334b263e41a@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>