kmod-setup: bypass heavy virtio-rng check if we are not running in a VM anyway

detect_vm() is cheap, because cached, let's hence do that early before
we get out the big guns and sweep through sysfs.

src/core/kmod-setup.c

@@ -67,6 +67,10 @@ static int has_virtio_rng_recurse_dir_cb(
 static bool has_virtio_rng(void) {
         int r;
 
+        /* Directory traversal might be slow, hence let's do a cheap check first if it's even worth it */
+        if (detect_vm() == VIRTUALIZATION_NONE)
+                return false;
+
         r = recurse_dir_at(
                         AT_FDCWD,
                         "/sys/devices/pci0000:00",