r6040: Fix multicast filter some more

This code has been broken forever, but in several different and
creative ways.

So far as I can work out, the R6040 MAC filter has 4 exact-match
entries, the first of which the driver uses for its assigned unicast
address, plus a 64-entry hash-based filter for multicast addresses
(maybe unicast as well?).

The original version of this code would write the first 4 multicast
addresses as exact-match entries from offset 1 (bug #1: there is no
entry 4 so this could write to some PHY registers).  It would fill the
remainder of the exact-match entries with the broadcast address (bug #2:
this would overwrite the last used entry).  If more than 4 multicast
addresses were configured, it would set up the hash table, write some
random crap to the MAC control register (bug #3) and finally walk off
the end of the list when filling the exact-match entries (bug #4).

All of this seems to be pointless, since it sets the promiscuous bit
when the interface is made promiscuous or if >4 multicast addresses
are enabled, and never clears it (bug #5, masking bug #2).

The recent(ish) changes to the multicast list fixed bug #4, but
completely removed the limit on iteration over the exact-match entries
(bug #6).

Bug #4 was reported as
<https://bugzilla.kernel.org/show_bug.cgi?id=15355> and more recently
as <http://bugs.debian.org/600155

>.  Florian Fainelli attempted to fix
these in commit 3bcf8229, but that
actually dealt with bugs #1-3, bug #4 having been fixed in mainline at
that point.

That commit fixes the most important current bug #6.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: stable@kernel.org [2.6.35 only]
Signed-off-by: David S. Miller <davem@davemloft.net>