Update the device state functionality of chan_local such that it will return

NOT_INUSE or INUSE when Local channels are in use as opposed to just UNKNOWN.
It will still return INVALID if the extension doesn't exist at all.
(issue #8048, patch from tim_ringenbach)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@62673 65c4cc65-6c06-0410-ace0-fbb531ad65f3