asterisk: Unsolicited MWI NOTIFY is broken

[cruzccl]

Once a user-terminal-extension relationship is made, module res_pjsip_mwi.so needs to be reloaded in order to make unsolicited MWI NOTIFY work.

Besides, once unsolicited MWI is working, changing a user extension breaks again until res_pjsip_mwi.so is reloaded.

Asterisk reloads res_pjsip_mwi.so when a contact is modified, but this never happens in IvozProvider as registers are kept in KamUsers.

This means that unsolicited MWI are broken for new relationships and extension changes until res_pjsip_mwi.so is (manually) reloaded or Asterisk is restarted.

[cruzccl]

After analyzing the Asterisk code related to unsolicited MWI, it seems that the module needs to be rewriten to work in IvozProvider, as Asterisk is not a registrar server and the trigger to update endpoint-voicemail relationship is never triggered.

In the future unsolicited MWI will be disabled and #14 will be implemented.

Until that point, res_pjsip_mwi.so module must be reloaded to have the relationship updated.