update netinet/udp.h for linux v4.18

add UDP_NO_CHECK6_* to restrict zero UDP6 checksums, new in linux commit
1c19448c9ba6545b80ded18488a64a7f3d8e6998 (pre-v4.18 change, was missed)
add UDP_SEGMENT to support generic segmentation offload for udp datagrams,
bec1f6f697362c5bc635dacd7ac8499d0a10a4e7 (new in v4.18)

include/netinet/udp.h

@@ -24,6 +24,9 @@ struct udphdr {
 
 #define UDP_CORK	1
 #define UDP_ENCAP	100
+#define UDP_NO_CHECK6_TX 101
+#define UDP_NO_CHECK6_RX 102
+#define UDP_SEGMENT	103
 
 #define UDP_ENCAP_ESPINUDP_NON_IKE 1
 #define UDP_ENCAP_ESPINUDP	2