interface: add support for extended addr while iface add

This patch adds support for given extended addr while adding a new interface.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
interface: mac: fix byteorder issues

The kernel except and delivers little endian byteorder. This patch fix
the current handling with byteorder.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>