Give the uplink modules short slugs, so their identity fits a backend's limit

Requiring wildcard-resolution gave each a consumer identity; mesh_<machine>_networkmanager is
over the 20 characters a backend keeps, and the anchor's declaration, which carries every
consumer's grant, could not be composed.

modules/networkmanager/module.json

@@ -1,6 +1,7 @@
 {
   "module": "networkmanager",
   "version": "1",
+  "slug": "nm",
   "requires": [
     "wildcard-resolution"
   ],