Update for Authorization header handling

- Correct challenge handling for REGISTER
- Add security_verify to subsequent REGISTER requests with cached authorization
- Add support to resend the cached Authorization header for INVITE
 
After properly set the initial registration outbound authentication credentials with e28a65c8555e206177265208a99d3ca0a6613d76,
the 401/407 challenge was handled by libpjsip and resend directly without noticing asterisk, which skipped all the process
that is expected to have within asterisk.
This fix keeps the challenge handling that made under libpjsip (to make the cached auth work) but avoid to resend directly
and invoke the callback function regardless the status of the challenge handling.