Update to v4.19 kernel headers.

Test: Builds and boots.
Change-Id: I99a9ed79666e143b47f02ca4e59eed94f69b7e4a
(cherry picked from commit a981e2e52e2e95a65fa9c9b6fb16dcb4c83dd576)
diff --git a/libc/kernel/uapi/linux/virtio_net.h b/libc/kernel/uapi/linux/virtio_net.h
index 329d736..07afd06 100644
--- a/libc/kernel/uapi/linux/virtio_net.h
+++ b/libc/kernel/uapi/linux/virtio_net.h
@@ -45,6 +45,7 @@
 #define VIRTIO_NET_F_GUEST_ANNOUNCE 21
 #define VIRTIO_NET_F_MQ 22
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23
+#define VIRTIO_NET_F_STANDBY 62
 #define VIRTIO_NET_F_SPEED_DUPLEX 63
 #ifndef VIRTIO_NET_NO_LEGACY
 #define VIRTIO_NET_F_GSO 6