support IFLA_VRF_PORT_TABLE attribute

Links that belong to a VRF carry the VRF table ID in the link info. For
a VRF link we already had these attributes:

```
LinkInfo([Kind(Vrf), Data(Vrf([TableId(10)]))])
```

For ports attached to a VRF we now have:

```
LinkInfo([Kind(Veth), PortKind(Vrf), PortData(VrfPort([TableId(10)]))])
```

This tells us that this veth interface belong to the VRF with table ID
10.

src/link/link_info/info_port.rs

@@ -7,10 +7,14 @@ use netlink_packet_utils::{
     DecodeError, Emitable, Parseable,
 };
 
-use super::super::{InfoBondPort, InfoBridgePort};
+use super::{
+    super::{InfoBondPort, InfoBridgePort},
+    InfoVrf,
+};
 
 const BOND: &str = "bond";
 const BRIDGE: &str = "bridge";
+const VRF: &str = "vrf";
 
 const IFLA_INFO_PORT_KIND: u16 = 4;
 const IFLA_INFO_PORT_DATA: u16 = 5;
@@ -20,6 +24,7 @@ const IFLA_INFO_PORT_DATA: u16 = 5;
 pub enum InfoPortKind {
     Bond,
     Bridge,
+    Vrf,
     Other(String),
 }
 
@@ -31,6 +36,7 @@ impl std::fmt::Display for InfoPortKind {
             match self {
                 Self::Bond => BOND,
                 Self::Bridge => BRIDGE,
+                Self::Vrf => VRF,
                 Self::Other(s) => s.as_str(),
             }
         )
@@ -42,6 +48,7 @@ impl Nla for InfoPortKind {
         let len = match self {
             Self::Bond => BOND.len(),
             Self::Bridge => BRIDGE.len(),
+            Self::Vrf => VRF.len(),
             Self::Other(s) => s.len(),
         };
         len + 1
@@ -51,6 +58,7 @@ impl Nla for InfoPortKind {
         let s = match self {
             Self::Bond => BOND,
             Self::Bridge => BRIDGE,
+            Self::Vrf => VRF,
             Self::Other(s) => s.as_str(),
         };
         buffer[..s.len()].copy_from_slice(s.as_bytes());
@@ -76,16 +84,20 @@ impl<'a, T: AsRef<[u8]> + ?Sized> Parseable<NlaBuffer<&'a T>> for InfoPortKind {
         Ok(match s.as_str() {
             BOND => Self::Bond,
             BRIDGE => Self::Bridge,
+            VRF => Self::Vrf,
             _ => Self::Other(s),
         })
     }
 }
 
+pub type InfoVrfPort = InfoVrf;
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 #[non_exhaustive]
 pub enum InfoPortData {
     BondPort(Vec<InfoBondPort>),
     BridgePort(Vec<InfoBridgePort>),
+    VrfPort(Vec<InfoVrfPort>),
     Other(Vec<u8>),
 }
 
@@ -94,6 +106,7 @@ impl Nla for InfoPortData {
         match self {
             Self::BondPort(nlas) => nlas.as_slice().buffer_len(),
             Self::BridgePort(nlas) => nlas.as_slice().buffer_len(),
+            Self::VrfPort(nlas) => nlas.as_slice().buffer_len(),
             Self::Other(bytes) => bytes.len(),
         }
     }
@@ -102,6 +115,7 @@ impl Nla for InfoPortData {
         match self {
             Self::BondPort(nlas) => nlas.as_slice().emit(buffer),
             Self::BridgePort(nlas) => nlas.as_slice().emit(buffer),
+            Self::VrfPort(nlas) => nlas.as_slice().emit(buffer),
             Self::Other(bytes) => buffer.copy_from_slice(bytes),
         }
     }
@@ -125,6 +139,10 @@ impl InfoPortData {
                 .map(|nla| nla.and_then(|nla| InfoBridgePort::parse(&nla)))
                 .collect::<Result<Vec<_>, _>>()
                 .map(InfoPortData::BridgePort),
+            InfoPortKind::Vrf => NlasIterator::new(payload)
+                .map(|nla| nla.and_then(|nla| InfoVrfPort::parse(&nla)))
+                .collect::<Result<Vec<_>, _>>()
+                .map(InfoPortData::VrfPort),
             InfoPortKind::Other(_) => Ok(InfoPortData::Other(payload.to_vec())),
         };