Replace __unused in linux/sysctl.h with __linux_unused

To avoid conflict with "#define __unused" in sys/cdefs.h

See
  https://android-review.googlesource.com/#/c/43479
  https://android-review.googlesource.com/#/c/43565

Change-Id: I6b8155570f4398b3ee8845d75bd231bca7f1d86f
diff --git a/ndk/platforms/android-3/include/linux/icmp.h b/ndk/platforms/android-3/include/linux/icmp.h
index c5b58bb..d69a0e2 100644
--- a/ndk/platforms/android-3/include/linux/icmp.h
+++ b/ndk/platforms/android-3/include/linux/icmp.h
@@ -66,7 +66,7 @@
  } echo;
  __u32 gateway;
  struct {
- __u16 __unused_field;
+ __u16 __linux_unused;
  __u16 mtu;
  } frag;
  } un;
diff --git a/ndk/platforms/android-3/include/linux/sysctl.h b/ndk/platforms/android-3/include/linux/sysctl.h
index 329e561..730c740 100644
--- a/ndk/platforms/android-3/include/linux/sysctl.h
+++ b/ndk/platforms/android-3/include/linux/sysctl.h
@@ -28,7 +28,7 @@
  size_t __user *oldlenp;
  void __user *newval;
  size_t newlen;
- unsigned long __unused[4];
+ unsigned long __linux_unused[4];
 };
 
 enum