k3s: add modprobe to k3s's PATH

Otherwise we get warnings like 'level=warning msg="failed to start
br_netfilter module"' in k3s's logs.

Adding modprobe to k3s's PATH fixes the warning at least. I'm not
certain if it fixes any real issue or not.

pkgs/applications/networking/cluster/k3s/default.nix

@@ -9,6 +9,7 @@
 , buildGoPackage
 , git
 , runc
+, kmod
 , libseccomp
 , pkgconfig
 , ethtool
@@ -226,6 +227,7 @@ stdenv.mkDerivation rec {
   # https://github.com/kubernetes/kubernetes/issues/26093#issuecomment-237202494
   # Note the list in that issue is stale and some aren't relevant for k3s.
   k3sRuntimeDeps = [
+    kmod
     socat
     iptables
     iproute