Make license renewal failure non-fatal until the end of the license duration

### [REQUIRED] Use case description
When the license is **really** expired we don't even pass the stream to ExoPlayer, we fire an error event instead. Now we also have to take this value into account, but it's a private constant (in DefaultDrmSession) so we can't. Hardcoding `60` (the current constant value) in our code seems like a bad idea because this value may change, at some point.

### Proposed solution
Move this value to the almighty C class (as public) - then we can read it.

### Alternatives considered
Hardcode this value in application code.