Fix deadlock in sig_pri when hanging up.

The pri_dchannel thread currently violates locking order by locking the private
and then attempting to queue a frame, which needs to lock the channel. Queueing
a frame is unneccesary though and is actually a regression since sig_pri.
All the places that currently use ast_softhangup_nolock now will just set the
softhangup value directly as before.

(closes issue #17216)
Reported by: lmsteffan
Patches: 
      bug17216.patch uploaded by jpeeler (license 325)



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@261866 65c4cc65-6c06-0410-ace0-fbb531ad65f3