Update to kernel headers v4.12.3.

Test: Built angler.
Change-Id: Icbcf4fac2334de8409b049ed7a3b4c24b4e98ce9
diff --git a/libc/kernel/uapi/linux/if_packet.h b/libc/kernel/uapi/linux/if_packet.h
index d800a8f..61d0a3a 100644
--- a/libc/kernel/uapi/linux/if_packet.h
+++ b/libc/kernel/uapi/linux/if_packet.h
@@ -72,6 +72,7 @@
 #define PACKET_FANOUT_CBPF 6
 #define PACKET_FANOUT_EBPF 7
 #define PACKET_FANOUT_FLAG_ROLLOVER 0x1000
+#define PACKET_FANOUT_FLAG_UNIQUEID 0x2000
 #define PACKET_FANOUT_FLAG_DEFRAG 0x8000
 struct tpacket_stats {
   unsigned int tp_packets;