The bootup of the armsr target sometimes failed like this:
```
[ 0.762283] NET: Registered PF_INET6 protocol family
[ 0.791987] workqueue: Failed to create a worker thread: -EAGAIN
[ 0.801986] workqueue: Failed to create a rescuer kthread for wq "mld": -EAGAIN
[ 0.964017] NET: Unregistered PF_INET6 protocol family
```
Increase the maximum number of threads the kernel allows.
Link: https://github.com/openwrt/openwrt/pull/19376
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
c5330bdf7e