disable check for swiotlb for kernels newer as 4.16 because it uses a symbol
that isn't exported anymore

--- kernel/common/inc/nv-linux.h.orig	2018-04-23 14:33:53.184275029 +0200
+++ kernel/common/inc/nv-linux.h	2018-04-23 15:26:38.892322165 +0200
@@ -1209,7 +1209,7 @@
 static inline NvBool nv_dma_maps_swiotlb(struct pci_dev *dev)
 {
     NvBool swiotlb_in_use = NV_FALSE;
-#if defined(CONFIG_SWIOTLB)
+#if defined(CONFIG_SWIOTLB) && LINUX_VERSION_CODE < KERNEL_VERSION(4, 16, 0)
   #if defined(NV_DMA_OPS_PRESENT) || defined(NV_GET_DMA_OPS_PRESENT)
     /*
      * We only use the 'dma_ops' symbol on older x86_64 kernels; later kernels,