macvlan: add FDB bridge ops and macvlan flags

This adds FDB bridge ops to the macvlan device passthru mode.
Additionally a flags field was added and a NOPROMISC bit to
allow users to use passthru mode without the driver calling
dev_set_promiscuity(). The flags field is a u16 placed in a
4 byte hole (consuming 2 bytes) of the macvlan_dev struct.

We want to do this so that the macvlan driver or stack
above the macvlan driver does not have to process every
packet. For the use case where we know all the MAC addresses
of the endstations above us this works well.

This patch is a result of Roopa Prabhu's work. Follow up
patches are needed for VEPA and VEB macvlan modes.

v2: Change from distinct nopromisc mode to a flags field to
    configure this. This avoids the tendency to add a new
    mode every time we need some slightly different behavior.
v3: fix error in dev_set_promiscuity and add change and get
    link attributes for flags.

CC: Roopa Prabhu <roprabhu@cisco.com>
CC: Michael S. Tsirkin <mst@redhat....