Update to v4.17.3 kernel headers.

Test: Builds, boots on a walleye.
Change-Id: I389d8b61ec00ea309e38d1b1a2e0dace48c21edb
diff --git a/libc/kernel/uapi/linux/openvswitch.h b/libc/kernel/uapi/linux/openvswitch.h
index bea44d0..1dba16e 100644
--- a/libc/kernel/uapi/linux/openvswitch.h
+++ b/libc/kernel/uapi/linux/openvswitch.h
@@ -204,6 +204,7 @@
   OVS_TUNNEL_KEY_ATTR_IPV6_SRC,
   OVS_TUNNEL_KEY_ATTR_IPV6_DST,
   OVS_TUNNEL_KEY_ATTR_PAD,
+  OVS_TUNNEL_KEY_ATTR_ERSPAN_OPTS,
   __OVS_TUNNEL_KEY_ATTR_MAX
 };
 #define OVS_TUNNEL_KEY_ATTR_MAX (__OVS_TUNNEL_KEY_ATTR_MAX - 1)