atp: remove set_rx_mode_8012()

Building atp.o triggers this GCC warning:
    drivers/net/ethernet/realtek/atp.c: In function ‘set_rx_mode’:
    drivers/net/ethernet/realtek/atp.c:871:26: warning: ‘mc_filter[0]’ may be used uninitialized in this function [-Wuninitialized]

GCC is correct. In promiscuous mode 'mc_filter' will be used
uninitialized in set_rx_mode_8012(), which is apparently inlined into
set_rx_mode().

But it turns out set_rx_mode_8012() will never be called, since
net_local.chip_type will always be RTL8002. So we can just remove
set_rx_mode_8012() and do some related cleanups.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>