Eliminate deadlock potential in dahdi_fixup().

Eliminate deadlock potential in dahdi_fixup().

(This is a backport of 269307, committed to trunk by rmudgett.)

Calling dahdi_indicate() when the channel private lock is already
held can cause a deadlock if the PRI lock is needed because
dahdi_indicate() will also get the channel private lock.  The pri_grab()
function assumes that the channel private lock is held once to avoid
deadlock.

(closes issue #17261)
Reported by: aragon

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@271335 65c4cc65-6c06-0410-ace0-fbb531ad65f3