Update to v5.8 kernel headers.

Kernel headers coming from:

Git: https://android.googlesource.com/kernel/common/
Branch: android-mainline
Tag: android-mainline-5.8

Test: NA
Change-Id: I2231c877589820fc09800a200cf4ac62ba74b04c
diff --git a/libc/kernel/uapi/linux/if.h b/libc/kernel/uapi/linux/if.h
index 0821f2b..63c77eb 100644
--- a/libc/kernel/uapi/linux/if.h
+++ b/libc/kernel/uapi/linux/if.h
@@ -114,6 +114,7 @@
 enum {
   IF_LINK_MODE_DEFAULT,
   IF_LINK_MODE_DORMANT,
+  IF_LINK_MODE_TESTING,
 };
 #if __UAPI_DEF_IF_IFMAP
 struct ifmap {