Upon shutdown, both drivers would attempt to power down external
interfaces, but never attempted to bring them back up when the span was
restarted. Removing that code allows the driver to work properly until
a better solution can be found.
git-svn-id: http://svn.asterisk.org/svn/dahdi/linux/trunk@9316 a0bf4364-ded3-4de4-8d8a-66a801d63aff