unix: add UDP socket option constants on linux

Change-Id: I4c947319f98754a5135b306d8ff042a986ab5440
Reviewed-on: https://go-review.googlesource.com/c/sys/+/484637
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>

unix/mkerrors.sh

@@ -204,6 +204,7 @@ struct ltchars {
 #include <sys/timerfd.h>
 #include <sys/uio.h>
 #include <sys/xattr.h>
+#include <netinet/udp.h>
 #include <linux/audit.h>
 #include <linux/bpf.h>
 #include <linux/can.h>
@@ -518,7 +519,7 @@ ccflags="$@"
 		$2 ~ /^LOCK_(SH|EX|NB|UN)$/ ||
 		$2 ~ /^LO_(KEY|NAME)_SIZE$/ ||
 		$2 ~ /^LOOP_(CLR|CTL|GET|SET)_/ ||
-		$2 ~ /^(AF|SOCK|SO|SOL|IPPROTO|IP|IPV6|TCP|MCAST|EVFILT|NOTE|SHUT|PROT|MAP|MFD|T?PACKET|MSG|SCM|MCL|DT|MADV|PR|LOCAL|TCPOPT)_/ ||
+		$2 ~ /^(AF|SOCK|SO|SOL|IPPROTO|IP|IPV6|TCP|MCAST|EVFILT|NOTE|SHUT|PROT|MAP|MFD|T?PACKET|MSG|SCM|MCL|DT|MADV|PR|LOCAL|TCPOPT|UDP)_/ ||
 		$2 ~ /^NFC_(GENL|PROTO|COMM|RF|SE|DIRECTION|LLCP|SOCKPROTO)_/ ||
 		$2 ~ /^NFC_.*_(MAX)?SIZE$/ ||
 		$2 ~ /^RAW_PAYLOAD_/ ||