Interrupt event example: be sure to specify INT3 explicitly to future-proof if additional interrupt events are supported
xen_events.c : upon delivery of an interrupt event, copy the interrupt value into the event structure for consumption by callback. Not strictly required, but useful to be explicit nevertheless.
xen_events.c : clarify in error message that INT3 reinjection errors are expected and benign for a range of Xen versions (bug described in comments).  If printed for a Xen version outside of that range, it is likely that the user is running an RC build or similar.
Return the offset on the GFN for interrupt events