[mod_sofia] fix missing auth challenge in 401 response

[greenbea]

Description

This commit fixes issues signalwire#1779 and signalwire#2640

The bug was caused by the incoming subscribe handler calling directly sofia_reg_parse_auth with an exptime of 0, causing the nonce to get deleted from the db after hitting the nonce_ttl time. That by itself was wrong since the exptime should have been exptime + nonce-ttl, but the main problem was that the handler returned a 401 without an auth challenge.

The fix was simple: instead of calling directly sofia_reg_parse_auth from the subscribe handler, it passes the authentication handling to the sofia_reg_handle_register the same way sofia_handle_sip_i_invite handler does.

Bugs I noticed on the way:

• Freeswitch in sofia_handle_sip_i_invite sets an exptime that is being used to calculate the nonce_ttl nonce_tll + exptime and takes exptime from the expires header or from the contact header if exists or to a default value of 300.
  1. freeswitch doesn't adhere to the sip-force-expires* settings (and to force-subscription-expires after this commit) when setting the exptime.
  2. INVITES doesn't have an expire header so nonce_ttl will always be nonce_ttl + 300
• freeswitch fires sofia::register_attempt and sofia::register_failure events on invites
• a lot of handling done in sofia_reg_handle_register_token is meant for registration and is being called for invites as well