Description of problem:
"ip -b" gets OOM-killed when adding routes with NetworkManager active.

Version-Release number of selected component (if applicable):
iproute-6.1.0-1.el9.x86_64

How reproducible:
frequently

Steps to Reproduce:
1. make sure that NetworkManager.service is active
2. prepare a routes file:
bird_routes.py testX6 6 $NUM > bird-routes
3. apply these commands:
ip -b bird-routes

Actual results:
on a machine with 4GB memory:

• NUM=100000 seems to pass always
• NUM between 400000 to 500000 sometimes works, sometimes OOMs
• NUM around one million or larger yields reliable OOM

OOM:
Mar 30 10:21:16 kernel: oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/user.slice/user-0.slice/session-3.scope,task=ip,pid=26861,uid=0
Mar 30 10:21:16 kernel: Out of memory: Killed process 26861 (ip) total-vm:26388012kB, anon-rss:3335200kB, file-rss:0kB, shmem-rss:0kB, UID:0 pgtables:51676kB oom_score_adj:0

Expected results:
ip does keeps reasonable memory usage

Additional info:

• similar behaviour is for IPv4 as well however large NUM is needed to make it visible
• generating script is as used in NetworkManager CI: https://gitlab.freedesktop.org/NetworkManager/NetworkManager-ci/-/blob/main/prepare/bird_routes.py
• we created this scenario as a verification of bug 1861527 to mimick environment of BGP routers (where 2M of routes per interface are nothing exceptional). Over time, the scenario started failing for unclear reasons which turned out to be this bug