Update to kernel headers v4.12.3.

Test: Built angler.
Change-Id: Icbcf4fac2334de8409b049ed7a3b4c24b4e98ce9
diff --git a/libc/kernel/uapi/linux/if_arp.h b/libc/kernel/uapi/linux/if_arp.h
index be3499d..9f056fb 100644
--- a/libc/kernel/uapi/linux/if_arp.h
+++ b/libc/kernel/uapi/linux/if_arp.h
@@ -82,6 +82,7 @@
 #define ARPHRD_IP6GRE 823
 #define ARPHRD_NETLINK 824
 #define ARPHRD_6LOWPAN 825
+#define ARPHRD_VSOCKMON 826
 #define ARPHRD_VOID 0xFFFF
 #define ARPHRD_NONE 0xFFFE
 #define ARPOP_REQUEST 1