ioc3-eth: store pointer to net_device for priviate area

Computing the alignment manually for going from priv to pub is probably
not such a good idea, and in general the assumption that going from priv
to pub is possible trivially could change, so rather than relying on
that, we change things to just store a pointer to pub. This was sugested
by DaveM in [1].

[1] http://www.spinics.net/lists/netdev/msg443992.html



Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>