cnxcc: don't terminate non confirmed calls

[linuxmaniac]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue cnxcc: when credit reach the limit non confirmed calls of the same customer fail to terminate #2346

Description

• non confirmed calls can't be terminated via dialog.terminate_dlg() API
• set call.max_amount to 0 to terminate the call if gets confirmed