unix: add Linux MPLS tunnel constants for use with rtnetlink APIs

Change-Id: Ic990c616c416e7bfe98e68eb74bab2810a1126ef
Reviewed-on: https://go-review.googlesource.com/c/sys/+/271137
Trust: Matt Layher <mdlayher@gmail.com>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/linux/types.go

diff --git a/unix/linux/types.go b/unix/linux/types.go
index 84c7c0d..b86df41 100644
--- a/unix/linux/types.go
+++ b/unix/linux/types.go
@@ -103,6 +103,7 @@
 #include <linux/keyctl.h>
 #include <linux/loop.h>
 #include <linux/lwtunnel.h>
+#include <linux/mpls_iptunnel.h>
 #include <linux/ncsi.h>
 #include <linux/net_namespace.h>
 #include <linux/net_tstamp.h>
@@ -2923,7 +2924,7 @@
 	PPS_FETCH     = C.PPS_FETCH
 )
 
-// lwtunnel APIs
+// lwtunnel and related APIs
 
 const (
 	LWTUNNEL_ENCAP_NONE       = C.LWTUNNEL_ENCAP_NONE
@@ -2936,4 +2937,9 @@
 	LWTUNNEL_ENCAP_SEG6_LOCAL = C.LWTUNNEL_ENCAP_SEG6_LOCAL
 	LWTUNNEL_ENCAP_RPL        = C.LWTUNNEL_ENCAP_RPL
 	LWTUNNEL_ENCAP_MAX        = C.LWTUNNEL_ENCAP_MAX
+
+	MPLS_IPTUNNEL_UNSPEC = C.MPLS_IPTUNNEL_UNSPEC
+	MPLS_IPTUNNEL_DST    = C.MPLS_IPTUNNEL_DST
+	MPLS_IPTUNNEL_TTL    = C.MPLS_IPTUNNEL_TTL
+	MPLS_IPTUNNEL_MAX    = C.MPLS_IPTUNNEL_MAX
 )

unix/ztypes_linux.go

diff --git a/unix/ztypes_linux.go b/unix/ztypes_linux.go
index 22e67b2..504ef13 100644
--- a/unix/ztypes_linux.go
+++ b/unix/ztypes_linux.go
@@ -2993,4 +2993,9 @@
 	LWTUNNEL_ENCAP_SEG6_LOCAL = 0x7
 	LWTUNNEL_ENCAP_RPL        = 0x8
 	LWTUNNEL_ENCAP_MAX        = 0x8
+
+	MPLS_IPTUNNEL_UNSPEC = 0x0
+	MPLS_IPTUNNEL_DST    = 0x1
+	MPLS_IPTUNNEL_TTL    = 0x2
+	MPLS_IPTUNNEL_MAX    = 0x2
 )