xen/evtchn: support more than 4096 ports

Remove the check during unbind for NR_EVENT_CHANNELS as this limits
support to less than 4096 ports.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index 5de2063..00f40f0 100644
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -417,7 +417,7 @@
 			break;
 
 		rc = -EINVAL;
-		if (unbind.port >= NR_EVENT_CHANNELS)
+		if (unbind.port >= xen_evtchn_nr_channels())
 			break;
 
 		rc = -ENOTCONN;