mv643xx_eth: fix multicast filter programming

mv643xx_eth: fix multicast filter programming

Commit 66e63ffbc04706568d8789cbb00eaa8ddbcae648 ("mv643xx_eth:
implement ->set_rx_mode()") cleaned up mv643xx_eth's multicast filter
programming, but broke it as well.

The non-special multicast filter table (for multicast addresses that
are not of the form 01:00:5e:00:00:xx) consists of 256 hash table
buckets organised as 64 32-bit words, where the 'accept' bits are
in the LSB of each byte, so in bits 24 16 8 0 of each 32-bit word.
The old code got this right, but the referenced commit broke this by
using bits 3 2 1 0 instead.  This commit fixes this up.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>