net: reorder struct netdev_hw_addr

Move 'synced' and 'global_use' fields before 'refcount', to shrinks
struct netdev_hw_addr by 8 bytes (on 64bit arches).

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>