Turn off hw.pci.intx_reroute in EC2

Having this enabled on Graviton systems prior to Graviton 4 results in
a resource leak and a kernel panic after repeated hotplug/unplug.

MFC after:	3 days
Sponsored by:	Amazon

release/tools/ec2.conf

@@ -79,6 +79,12 @@ ec2_common() {
 	# delay before rescanning upon device detach.
 	echo 'debug.acpi.quirks="56"' >> ${DESTDIR}/boot/loader.conf
 
+	# The default behaviour of re-routing INTx interrupts causes a
+	# resource leak on INTRng (aka on Graviton systems).  Repeated
+	# hotplug/unplug on PCI (not PCIe) Graviton systems ends up with
+	# a kernel panic unless we disable this.
+	echo 'hw.pci.intx_reroute=0' >> ${DESTDIR}/boot/loader.conf
+
 	# Load the kernel module for the Amazon "Elastic Network Adapter"
 	echo 'if_ena_load="YES"' >> ${DESTDIR}/boot/loader.conf