iptun: add support to ipip, ipip6 and ip6ip6 tunnels

[ffmancera]

All these tunnels use the IFLA_IPTUN_* netlink API. Therefore, both IFLAN_INFO_KIND "ipip" and "ip6tnl" data is serialized using the IpTun struct.

Unit tests added.

[cathay4t]

I think we should do ParseableParametrized with InfoKind as argument because IFLA_IPTUN_FLAGS has different size:

net/ipv6/ip6_tunnel.c
1992:	if (data[IFLA_IPTUN_FLAGS])
1993:		parms->flags = nla_get_u32(data[IFLA_IPTUN_FLAGS]);
2099:		/* IFLA_IPTUN_FLAGS */
2129:	    nla_put_u32(skb, IFLA_IPTUN_FLAGS, parm->flags) ||
2165:	[IFLA_IPTUN_FLAGS]		= { .type = NLA_U32 },

net/ipv6/sit.c
1664:		/* IFLA_IPTUN_FLAGS */
1704:	    nla_put_be16(skb, IFLA_IPTUN_FLAGS,
1744:	[IFLA_IPTUN_FLAGS]		= { .type = NLA_U16 },

[liangwen12year]

@ffmancera , can you apply the followin patch? Thanks!

commit 88882770944e6aa034d29cf9eb2e28c41a2d33a1
Author: Wen Liang <[email protected]>
Date:   Sun May 18 20:46:09 2025 -0400

    fixup! iptunnel: add support to ipip, ipip6 and ip6ip6 tunnels

diff --git a/src/link/link_info/info_data.rs b/src/link/link_info/info_data.rs
index d0d902e..e26930b 100644
--- a/src/link/link_info/info_data.rs
+++ b/src/link/link_info/info_data.rs
@@ -4,7 +4,7 @@ use anyhow::Context;
 
 use netlink_packet_utils::{
     nla::{Nla, NlaBuffer, NlasIterator},
-    DecodeError, Emitable, Parseable,
+    DecodeError, Emitable, Parseable, ParseableParametrized,
 };
 
 use super::super::{
@@ -362,7 +362,8 @@ impl InfoData {
                     let nla = &nla.context(format!(
                         "invalid IFLA_INFO_DATA for {kind} {payload:?}"
                     ))?;
-                    let parsed = InfoIpTunnel::parse(nla)?;
+                    let parsed =
+                        InfoIpTunnel::parse_with_param(nla, kind.clone())?;
                     v.push(parsed);
                 }
                 InfoData::IpTunnel(v)
diff --git a/src/link/link_info/iptunnel.rs b/src/link/link_info/iptunnel.rs
index 7ab50f2..04af70a 100644
--- a/src/link/link_info/iptunnel.rs
+++ b/src/link/link_info/iptunnel.rs
@@ -8,7 +8,7 @@ use byteorder::{ByteOrder, NativeEndian};
 use netlink_packet_utils::{
     nla::{DefaultNla, Nla, NlaBuffer},
     parsers::{parse_u16, parse_u32, parse_u8},
-    traits::Parseable,
+    traits::{Parseable, ParseableParametrized},
     DecodeError,
 };
 
@@ -146,8 +146,13 @@ impl Nla for InfoIpTunnel {
     }
 }
 
-impl<'a, T: AsRef<[u8]> + ?Sized> Parseable<NlaBuffer<&'a T>> for InfoIpTunnel {
-    fn parse(buf: &NlaBuffer<&'a T>) -> Result<Self, DecodeError> {
+impl<'a, T: AsRef<[u8]> + ?Sized>
+    ParseableParametrized<NlaBuffer<&'a T>, super::InfoKind> for InfoIpTunnel
+{
+    fn parse_with_param(
+        buf: &NlaBuffer<&'a T>,
+        kind: super::InfoKind,
+    ) -> Result<Self, DecodeError> {
         use self::InfoIpTunnel::*;
         let payload = buf.value();
         Ok(match buf.kind() {
@@ -204,9 +209,23 @@ impl<'a, T: AsRef<[u8]> + ?Sized> Parseable<NlaBuffer<&'a T>> for InfoIpTunnel {
                 parse_u32(payload)
                     .context("invalid IFLA_IPTUN_FLOWINFO value")?,
             ),
-            IFLA_IPTUN_FLAGS => Flags(TunnelFlags::from_bits_retain(
-                parse_u32(payload).context("invalid IFLA_IPTUN_FLAGS value")?,
-            )),
+            IFLA_IPTUN_FLAGS => match kind {
+                super::InfoKind::SitTun => {
+                    // Parse as u16 for SIT tunnels
+                    Flags(TunnelFlags::from_bits_retain(
+                        parse_u16(payload)
+                            .context("invalid IFLA_IPTUN_FLAGS value for SIT")?
+                            as u32,
+                    ))
+                }
+                _ => {
+                    // Default: parse as u32 for other tunnel types
+                    Flags(TunnelFlags::from_bits_retain(
+                        parse_u32(payload)
+                            .context("invalid IFLA_IPTUN_FLAGS value")?,
+                    ))
+                }
+            },
             IFLA_IPTUN_PROTO => Protocol(IpProtocol::from(
                 parse_u8(payload).context("invalid IFLA_IPTUN_PROTO value")?
                     as i32,