[VLAN]: set_rx_mode support for unicast address list

Reuse the existing logic for multicast list synchronization for the
unicast address list. The core of dev_mc_sync/unsync are split out as
__dev_addr_sync/unsync and moved from dev_mcast.c to dev.c.  These are
then used to implement dev_unicast_sync/unsync as well.

I'm working on cleaning up Intel's FCoE stack, which generates new MAC
addresses from the fibre channel device id assigned by the fabric as
per the current draft specification in T11.  When using such a
protocol in a VLAN environment it would be nice to not always be
forced into promiscuous mode, assuming the underlying Ethernet driver
supports multiple unicast addresses as well.

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>