[E1000]: Secondary unicast address support

Add support for configuring secondary unicast addresses. Unicast
addresses take precendece over multicast addresses when filling
the exact address filters to avoid going to promiscous mode.
When more unicast addresses are present than filter slots,
unicast filtering is disabled and all slots can be used for
multicast addresses.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>