Update to v4.19 kernel headers.

Test: Builds and boots.
Change-Id: I99a9ed79666e143b47f02ca4e59eed94f69b7e4a
diff --git a/libc/kernel/uapi/linux/netconf.h b/libc/kernel/uapi/linux/netconf.h
index 4f86757..27d3854 100644
--- a/libc/kernel/uapi/linux/netconf.h
+++ b/libc/kernel/uapi/linux/netconf.h
@@ -32,6 +32,7 @@
   NETCONFA_PROXY_NEIGH,
   NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
   NETCONFA_INPUT,
+  NETCONFA_BC_FORWARDING,
   __NETCONFA_MAX
 };
 #define NETCONFA_MAX (__NETCONFA_MAX - 1)