sfc: don't read beyond unicast address list

[ Upstream commit c70d68150f71b84cea6997a53493e17bf18a54db ]

If we have more than 32 unicast MAC addresses assigned to an interface
we will read beyond the end of the address table in the driver when
adding filters. The next 256 entries store multicast addresses, so we
will end up attempting to insert duplicate filters, which is mostly
harmless. If we add more than 288 unicast addresses we will then read
past the multicast address table, which is likely to be more exciting.

Fixes: 12fb0da4 ("sfc: clean fallbacks between promisc/normal in efx_ef10_filter_sync_rx_mode")
Signed-off-by: Bert Kenward <bkenward@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>