units: check if kmod command exists

We already check existences of quotaon in quotaon@.service and
quotacheck in systemd-quotacheck@.service.
Let's also check if kmod command exists.

Closes #38179.

units/kmod-static-nodes.service.in

@@ -13,6 +13,7 @@ DefaultDependencies=no
 Before=sysinit.target systemd-tmpfiles-setup-dev-early.service
 ConditionCapability=CAP_SYS_MODULE
 ConditionFileNotEmpty=/lib/modules/%v/modules.devname
+ConditionPathExists={{KMOD}}
 
 [Service]
 Type=oneshot