- Add the function linphone_address_equal().
- The comparison of two proxy config addresses now returns one of these three values: equal, weak-equal or different.
- If the new proxy config identity is equal to the previous one, a call to linphone_proxy_config_done() does not
unregister and does not delete the sal op. If it's weak-equal the sal op is destroyed but the unregister is not
done. Finally, if it's different the unregister is performed and the sal op is destroyed.