New issue by cryptarch on void-packages repository

https://github.com/void-linux/void-packages/issues/29468

Description:
Hi,

(This should probably go upstream, but it's not clear whether iproute2 bug reports are welcome on the [netdev mailing list](http://vger.kernel.org/vger-lists.html#netdev). So I thought I'd start here because I first noticed the problem when pulling in iproute 5.11.0 on one of my Void Linux boxen today.)

### System

* xuname:  `Void 5.10.23_1 x86_64 AuthenticAMD uptodate rrrmFFFFFFF`
* package: `iproute2-5.11.0_1`

### Expected behavior

Iproute2 batch mode should be able to build a working network namespace. See below in "how to reproduce" section for the example script `netns-test.sh`.

Expected usage and output (works in 5.10.0):

```
$ sudo ./bin/netns-test.sh
$ sudo ip netns exec netns-test ip route
default via 192.168.5.1 dev netns-test-1
192.168.0.0/24 via 192.168.5.1 dev netns-test-1
192.168.5.0/24 dev netns-test-1 proto kernel scope link src 192.168.5.2
192.168.5.1 dev netns-test-1 proto kernel scope link src 192.168.5.2
```

### Actual behavior

The inner veth doesn't come up properly:

```
$ sudo ./bin/netns-test.sh
$ sudo ip netns exec netns-test ip route
$ sudo ip netns exec netns-test ip link
Password:
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
39: netns-test-1@if40: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 1a:96:4e:4f:84:31 brd ff:ff:ff:ff:ff:ff link-netnsid 0
```

### Steps to reproduce the behavior

Put this into a script such as `~/bin/netns-test.sh`:

```
#! /bin/bash

gw=192.168.5.1
ip=192.168.5.2
ns=netns-test
veth0=${ns}-0
veth1=${ns}-1
/usr/local/sbin/ip -b - << EOF
link add $veth0 type veth peer name $veth1
addr add $gw peer $ip dev $veth0
link set dev $veth0 up
netns add $ns
link set $veth1 netns $ns
netns exec $ns ip link set dev lo up
netns exec $ns ip link set dev $veth1 up
netns exec $ns ip addr add $ip/24 dev $veth1
netns exec $ns ip addr add $ip peer $gw dev $veth1
netns exec $ns ip route add default via $gw dev $veth1
netns exec $ns ip route add 192.168.0.0/24 via $gw dev $veth1
EOF
```

Run the script and then check whether it works with commands such as `ip netns exec netns-test ip link` and `ip netns exec netns-test ip route`.

Note that `git bisect` identifies `1d9a81b8c9f30f9f4abeb875998262f61bf10577` as the offending commit.