xen/events: increment refcnt only if event channel is refcounted

xen/events: increment refcnt only if event channel is refcounted

In bind_evtchn_to_irq_chip() don't increment the refcnt of the event
channel blindly. In case the event channel is NOT refcounted, issue a
warning instead.

Add an additional safety net by doing the refcnt increment only if the
caller has specified IRQF_SHARED in the irqflags parameter.

Fixes: 9e90e58c11b7 ("xen: evtchn: Allow shared registration of IRQ handers")
Signed-off-by: Juergen Gross <[email protected]>
Reviewed-by: Oleksandr Tyshchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Juergen Gross <[email protected]>