zebra: Fix missing VRF flag

When `ip link del vrf1`, `zebra` have wrongly forgot it is a vrf type.
It thought it is a normal interface.

```
ZEBRA: [KMXEB-K771Y] netlink_parse_info: netlink-listen (NS 0) type RTM_DELLINK(17), len=588, seq=0, pid=0
ZEBRA: [TDJW2-B9KJW] RTM_DELLINK for vrf1(93) <- Wrongly as normal interface, not vrf
ZEBRA: [WEEJX-M4HA0] interface vrf1 vrf vrf1(93) index 93 is now inactive.
ZEBRA: [NXAHW-290AC] MESSAGE: ZEBRA_INTERFACE_DELETE vrf1 vrf vrf1(93)
ZEBRA: [H97XA-ABB3A] MESSAGE: ZEBRA_INTERFACE_VRF_UPDATE/DEL vrf1 VRF Id 93 -> 0
ZEBRA: [HP8PZ-7D6D2] MESSAGE: ZEBRA_INTERFACE_VRF_UPDATE/ADD vrf1 VRF Id 93 -> 0 <-
ZEBRA: [Y6R2N-EF2N4] interface vrf1 is being deleted from the system
ZEBRA: [KNFMR-AFZ53] RTM_DELLINK for VRF vrf1(93)
ZEBRA: [P0CZ5-RF5FH] VRF vrf1 id 93 is now inactive
ZEBRA: [XC3P3-1DG4D] MESSAGE: ZEBRA_VRF_DELETE vrf1
ZEBRA: [ZMS2F-6K837] VRF vrf1 id 4294967295 deleted
OSPF: [JKWE3-97M3J] Zebra: interface add vrf1 vrf default[0] index 0 flags 480 metric 0 mtu 65575 speed 0 <- Wrongly add interface
```

It triggers problems on clients.

It will kept as an normal interface in 'show run' after even completely removed,
as said in PR #13388. The clients will accept this wrong interface as normal,
not vrf type:

```
interface vrf1
exit
```
Or

```
interface vrf1
 ip ospf network broadcast
exit
```

The root cause is that the `ifp->status`'s `ZEBRA_INTERFACE_VRF_LOOPBACK`
flag of this vrf is cleared too early. After that clear, `zebra` ( and
then clients ) will take it as normal interface. So, move it from "vrf1"
to "default" VRF, then an unexpected interface with wrong `ifp->status`
is created.

Two changes to fix it:

1. Put the deletion of this flag at the last.
   Aim at that clients can get correct `ifp->status`.

2. Skip the procedure of switching VRF for interfaces of vrf type
   Don't send `ZEBRA_INTERFACE_ADD` to clients when deleting vrf.

Signed-off-by: anlan_cs <[email protected]>

zebra/if_netlink.c

@@ -2323,8 +2323,6 @@ int netlink_link_change(struct nlmsghdr *h, ns_id_t ns_id, int startup)
 			zlog_debug("RTM_DELLINK for %s(%u)", name,
 				   ifp->ifindex);
 
-		UNSET_FLAG(ifp->status, ZEBRA_INTERFACE_VRF_LOOPBACK);
-
 		if (IS_ZEBRA_IF_BOND(ifp))
 			zebra_l2if_update_bond(ifp, false);
 		if (IS_ZEBRA_IF_BOND_SLAVE(ifp))

zebra/interface.c

@@ -800,6 +800,8 @@ void if_delete_update(struct interface **pifp)
 	if (ifp->vrf->vrf_id && !vrf_is_backend_netns())
 		if_handle_vrf_change(ifp, VRF_DEFAULT);
 
+	UNSET_FLAG(ifp->status, ZEBRA_INTERFACE_VRF_LOOPBACK);
+
 	/* Reset some zebra interface params to default values. */
 	zif = ifp->info;
 	if (zif) {
@@ -840,6 +842,9 @@ void if_handle_vrf_change(struct interface *ifp, vrf_id_t vrf_id)
 	/* This is to issue an UPDATE or a DELETE, as appropriate. */
 	zebra_interface_vrf_update_del(ifp, vrf_id);
 
+	if (if_is_vrf(ifp))
+		return;
+
 	/* update VRF */
 	if_update_to_new_vrf(ifp, vrf_id);