kernel: enlarge offset to rootfs, disable sysfs devlink

the ag71xx driver doesn't probe with fw_devlink enabled

modules/base.nix

@@ -67,6 +67,7 @@ in {
     };
     boot.commandLine = [
       "earlyprintk=serial,ttyS0 console=ttyS0,115200 panic=10 oops=panic init=/bin/init loglevel=8 rootfstype=squashfs"
+      "fw_devlink=off"
     ];
     users.root = {
       uid = 0; gid= 0; gecos = "Root of all evaluation";