Update to kernel headers v5.2.6.

Also, fix a bug in update_all.py when the syscalls file does not change.

Test: Builds and boots on a taimen.
Change-Id: If85b00daef2c176f804a0861894f5bbca9c6d5df
diff --git a/libc/kernel/uapi/linux/version.h b/libc/kernel/uapi/linux/version.h
index 815f53d..94bf4ba 100644
--- a/libc/kernel/uapi/linux/version.h
+++ b/libc/kernel/uapi/linux/version.h
@@ -16,5 +16,5 @@
  ***
  ****************************************************************************
  ****************************************************************************/
-#define LINUX_VERSION_CODE 328192
+#define LINUX_VERSION_CODE 328198
 #define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))