fine-tune meso-impatience at roundabouts

[namdre]

In #5830 meso-impatience was introduced (ignore foes at max impatience) and in #14129 this was disabled for roundabouts to avoid jamming.

Traffic flow in meso may potentially be improved by permitting meso-impatience in roundabouts as long as the inside edge would not exceed the jam threshold with the entering vehicle + the ignored inside vehicle