conf: validate that PCI controller index is < 256

This is the maximum for many reasons, for starters because index ==
bus number, and a controller's bus number is 8 bits.

This incidentally resolves: https://bugzilla.redhat.com/1329090

src/conf/domain_conf.c

@@ -4897,6 +4897,21 @@ virDomainNetDefValidate(const virDomainNetDef *net)
 }
 
 
+static int
+virDomainControllerDefValidate(const virDomainControllerDef *controller)
+{
+    if (controller->type == VIR_DOMAIN_CONTROLLER_TYPE_PCI) {
+        if (controller->idx > 255) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("PCI controller index %d too high, maximum is 255"),
+                           controller->idx);
+            return -1;
+        }
+    }
+    return 0;
+}
+
+
 static int
 virDomainDeviceDefValidateInternal(const virDomainDeviceDef *dev,
                                    const virDomainDef *def)
@@ -4911,6 +4926,9 @@ virDomainDeviceDefValidateInternal(const virDomainDeviceDef *dev,
     case VIR_DOMAIN_DEVICE_NET:
         return virDomainNetDefValidate(dev->data.net);
 
+    case VIR_DOMAIN_DEVICE_CONTROLLER:
+        return virDomainControllerDefValidate(dev->data.controller);
+
     case VIR_DOMAIN_DEVICE_LEASE:
     case VIR_DOMAIN_DEVICE_FS:
     case VIR_DOMAIN_DEVICE_INPUT:
@@ -4918,7 +4936,6 @@ virDomainDeviceDefValidateInternal(const virDomainDeviceDef *dev,
     case VIR_DOMAIN_DEVICE_VIDEO:
     case VIR_DOMAIN_DEVICE_HOSTDEV:
     case VIR_DOMAIN_DEVICE_WATCHDOG:
-    case VIR_DOMAIN_DEVICE_CONTROLLER:
     case VIR_DOMAIN_DEVICE_GRAPHICS:
     case VIR_DOMAIN_DEVICE_HUB:
     case VIR_DOMAIN_DEVICE_SMARTCARD: