Remove support for pre-4.0.0 kernels.

Signed-off-by: Wren Turkal <wt@penguintechs.org>

v4l2loopback.c

@@ -33,8 +33,8 @@
 #include <linux/miscdevice.h>
 #include "v4l2loopback.h"
 
-#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 6, 1)
-#error This module is not supported on kernels before 3.6.1.
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 0, 0)
+#error This module is not supported on kernels before 4.0.0.
 #endif
 
 #if defined(timer_setup) && defined(from_timer)
@@ -94,14 +94,8 @@ MODULE_LICENSE("GPL");
 
 static inline void v4l2l_get_timestamp(struct v4l2_buffer *b)
 {
-	/* ktime_get_ts is considered deprecated, so use ktime_get_ts64 if possible */
-#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 17, 0)
-	struct timespec ts;
-	ktime_get_ts(&ts);
-#else
 	struct timespec64 ts;
 	ktime_get_ts64(&ts);
-#endif
 
 	b->timestamp.tv_sec = ts.tv_sec;
 	b->timestamp.tv_usec = (ts.tv_nsec / NSEC_PER_USEC);
@@ -2501,18 +2495,10 @@ static void init_vdev(struct video_device *vdev, int nr)
 #endif
 
 	if (debug > 1)
-#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 20, 0)
-		vdev->debug = V4L2_DEBUG_IOCTL | V4L2_DEBUG_IOCTL_ARG;
-#else
 		vdev->dev_debug = V4L2_DEV_DEBUG_IOCTL |
 				  V4L2_DEV_DEBUG_IOCTL_ARG;
-#endif
 
-		/* since kernel-3.7, there is a new field 'vfl_dir' that has to be
-	 * set to VFL_DIR_M2M for bidirectional devices */
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 7, 0)
 	vdev->vfl_dir = VFL_DIR_M2M;
-#endif
 
 	MARK();
 }