[asterisk-ss7] Fix for when charge indicator is "no charge"

[Juan Carlos Castro y Castro]

Correction... "it abstains from forwarding the answer frame if the 
previously recorded value was 1 (no charge)." The patch was correct, 
only the message text was wrong.

Juan Carlos Castro y Castro
Instant Solution Ltda. <http://www.instant.com.br/>
Rio de Janeiro - Brazil

Juan Carlos Castro y Castro escreveu:
> Currently chan_ss7 doesn't give a cow when the caller gets a "no 
> charge" in the backwards call indicator field and sends an answer 
> frame to the calling channel in any case. I made this patch to fix it. 
> It just records the charge indicator received in the ACM response in a 
> field in the pvt struct, and when the ANM arrives, it abstains from 
> forwarding the answer frame if the previously recorded value was 2 (no 
> charge).
>
> I tested it calling an invalid number from a SIP ATA and it works OK. 
> I hear the other phone company's recording as early media and the call 
> is no longer billed. I tested in 0.9, but the patch applies to 1.0.0 too.
>
> This patch is GPL v2 and (C) Instant Solutions Ltda. of Brazil.