sphone: use ringing volume specified in profile, instead of media volume

[sicelo]

When on the desktop, it is possible to adjust the media volume level using the volume keys. This can also happen accidentally. Additionally, this works even while the screen is locked!

On an incoming call, if the media volume was low enough, the ringtone will be barely audible, leading to missed calls.

Therefore, sphone should use a ringing volume derived from the active profile (silent, general, etc.), not the media volume.