Fixup some skinny bugs causing Fracks and ao2 cleanup issues.

Moved channel locking into setsubstate so that a process can complete
working on a sub before another starts changing it. The existing code
was causing some Fracks with schedule deletion.

Removed multiple rtp cleanup. Now only cleansup up once, fixing ao2 
object cleanup issues.
........

Merged revisions 404306 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@404307 f38db490-d61c-443f-a65b-d21fe96a405b