add PACKET_IGNORE_OUTGOING sockopt from linux v4.20

new in linux commit fa788d986a3aac5069378ed04697bd06f83d3488

include/netpacket/packet.h

@@ -48,6 +48,7 @@ struct packet_mreq {
 #define PACKET_QDISC_BYPASS		20
 #define PACKET_ROLLOVER_STATS		21
 #define PACKET_FANOUT_DATA		22
+#define PACKET_IGNORE_OUTGOING		23
 
 #define PACKET_MR_MULTICAST	0
 #define PACKET_MR_PROMISC	1