BIRD crashes on OSPF reconfiguration

[Nicolas Devos]

Hello,

I tested the `ip-iface-crash` branch, with success!
The logs/prompts are pasted below. 
As can be seen, the configuration is successfully switched multiple times.


```
# birdc
BIRD 3.1.4+branch.ip.iface.crash.81ab0c5b006a ready.
# birdc 'configure soft "/tmp/ospf/ospf-1.conf"'
BIRD 3.1.4+branch.ip.iface.crash.81ab0c5b006a ready.
Reading configuration from /tmp/ospf/ospf-1.conf
Reconfigured
# birdc 'configure soft "/tmp/ospf/ospf-2.conf"'
BIRD 3.1.4+branch.ip.iface.crash.81ab0c5b006a ready.
Reading configuration from /tmp/ospf/ospf-2.conf
Reconfigured
# birdc 'configure soft "/tmp/ospf/ospf-1.conf"'
BIRD 3.1.4+branch.ip.iface.crash.81ab0c5b006a ready.
Reading configuration from /tmp/ospf/ospf-1.conf
Reconfigured
# birdc 'configure soft "/tmp/ospf/ospf-2.conf"'
BIRD 3.1.4+branch.ip.iface.crash.81ab0c5b006a ready.
Reading configuration from /tmp/ospf/ospf-2.conf
Reconfigured
```


```
# ./bird -u bird -g bird -c /opt/bird/bird.conf -s/var/run/bird/bird.ctl -d
bird: 2025-11-03 05:23:46.578 [0001]  Chosen router ID 10.89.112.123 according to interface enp6s0
bird: 2025-11-03 05:23:46.578 [0001]  Started
bird: 2025-11-03 05:24:27.938 [0001]  Reconfiguring
bird: 2025-11-03 05:24:27.938 [0001]  Adding protocol ospf1
bird: 2025-11-03 05:24:27.954 [0001]  Reconfigured
bird: 2025-11-03 05:24:33.768 [0001]  Reconfiguring
bird: 2025-11-03 05:24:33.769 [0001]  ospf1: Restarting interface enp11s0.3676 (172.21.8.0/28) in area 0.0.0.1
bird: 2025-11-03 05:24:33.769 [0001]  Reconfigured
bird: 2025-11-03 05:28:42.624 [0001]  Reconfiguring
bird: 2025-11-03 05:28:42.625 [0001]  ospf1: Restarting interface enp11s0.3676 (172.21.8.0/28) in area 0.0.0.1
bird: 2025-11-03 05:28:42.625 [0001]  Reconfigured
bird: 2025-11-03 05:28:45.170 [0001]  Reconfiguring
bird: 2025-11-03 05:28:45.171 [0001]  ospf1: Restarting interface enp11s0.3676 (172.21.8.0/28) in area 0.0.0.1
bird: 2025-11-03 05:28:45.171 [0001]  Reconfigured
```


Kind regards,
Nicolas