app_meetme: Fix overwrite of DAHDI conference data structure.

Starting a conference recording using the admin menu overwrites the DAHDI
conference data structure used to modify the admin user's conference mute
mode.

* Made no longer pass the user's DAHDI conference data structure into the
menu functions.  The menu now uses its own DAHDI conference data
structure to start the recording channel.

* Moved the unlock conf->playlock to before playing the conf-full message.
No sense keeping the lock while that prompt is playing.  The user is never
going to get into the conference at that point.


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@413991 f38db490-d61c-443f-a65b-d21fe96a405b