net: export NET_ADDR_* values to user-space API

NET_ADDR_* values are exported in the
/sys/class/net/<iface>/addr_assign_type sysfs attributes, and as such
constitutes an user-space ABI. Move the NET_ADDR_* definitions from
include/linux/netdevice.h to include/uapi/linux/netdevice.h

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>