accountcode: Slightly change accountcode propagation.

The previous behavior was to simply set the accountcode of an outgoing
channel to the accountcode of the channel initiating the call.  It was
done this way a long time ago to allow the accountcode set on the SIP/100
channel to be propagated to a local channel so the dialplan execution on
the Local;2 channel would have the SIP/100 accountcode available.

SIP/100 -> Local;1/Local;2 -> SIP/200

Propagating the SIP/100 accountcode to the local channels is very useful.
Without any dialplan manipulation, all channels in this call would have
the same accountcode.

Using dialplan, you can set a different accountcode on the SIP/200 channel
either by setting the accountcode on the Local;2 channel or by the Dial
application's b(pre-dial), M(macro) or U(gosub) options, or by the
FollowMe application's b(pre-dial) option, or by the Queue application's
macro or gosub options.  Before Asterisk v12, the altered accountcode on
SIP/200 will remain until the local channels optimize out and the
accountcode would change to the SIP/100 accountcode.

Asterisk v1.8 attempted to add peeraccount support but ultimately had to
punt on the support.  The peeraccount support was rendered useless because
of how the CDR code needed to unconditionally force the caller's
accountcode onto the peer channel's accountcode.  The CEL events were thus
intentionally made to always use the channel's accountcode as the
peeraccount value.

With the arrival of Asterisk v12, the situation has improved somewhat so
peeraccount support can be made to work.  Using the indicated example, the
the accountcode values become as follows when the peeraccount is set on
SIP/100 before calling SIP/200:

SIP/100 ---> Local;1 ---- Local;2 ---> SIP/200
acct: 100 \/ acct: 200 \/ acct: 100 \/ acct: 200
peer: 200 /\ peer: 100 /\ peer: 200 /\ peer: 100

If a channel already has an accountcode it can only change by the
following explicit user actions:

1) A channel originate method that can specify an accountcode to use.

2) The calling channel propagating its non-empty peeraccount or its
non-empty accountcode if the peeraccount was empty to the outgoing
channel's accountcode before initiating the dial.  e.g., Dial and
FollowMe.  The exception to this propagation method is Queue.  Queue will
only propagate peeraccounts this way only if the outgoing channel does not
have an accountcode.

3) Dialplan using CHANNEL(accountcode).

4) Dialplan using CHANNEL(peeraccount) on the other end of a local
channel pair.

If a channel does not have an accountcode it can get one from the
following places:

1) The channel driver's configuration at channel creation.

2) Explicit user action as already indicated.

3) Entering a basic or stasis-mixing bridge from a peer channel's
peeraccount value.

You can specify the accountcode for an outgoing channel by setting the
CHANNEL(peeraccount) before using the Dial, FollowMe, and Queue
applications.  Queue adds the wrinkle that it will not overwrite an
existing accountcode on the outgoing channel with the calling channels
values.

Accountcode and peeraccount values propagate to an outgoing channel before
dialing.  Accountcodes also propagate when channels enter or leave a basic
or stasis-mixing bridge.  The peeraccount value only makes sense for
mixing bridges with two channels; it is meaningless otherwise.

* Made peeraccount functional by changing accountcode propagation as
described above.

* Fixed CEL extracting the wrong ie value for the peeraccount.  This was
done intentionally in Asterisk v1.8 when that version had to punt on
peeraccount.

* Fixed a few places dealing with accountcodes that were reading from
channels without the lock held.

AFS-65 #close

Review: https://reviewboard.asterisk.org/r/3601/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@419520 f38db490-d61c-443f-a65b-d21fe96a405b