VoIP: increase call invite life time

[manuroe]

Users complain that they do not have enough time to answer to a call.

The caller currently gives a 30s lifetime for the call invite. This time starts from the moment the HS acknowledges the sending of the call invite event. Once the time is elapsed, the caller ends the call.
This lifetime does not take care if the callee gets notified for the call.

This lifetime may be short because of:

• network latency for the call event notification to go from the callee HS to his matrix app
• the callee matrix app needs to wakeup (Riot store is slow to load for heavy users)
• the callee matrix app needs to sync with the callee HS to get the call event

[manuroe]

Let's increase the lifetime to 60s.