Revert "Disable networking-l2gw in scenario004"

This reverts commit 06ed08b59a.

Reason for revert:
The original problem was resolved by the dependent patch.

Depends-on: https://review.opendev.org/c/x/networking-l2gw/+/845141
Related-Bug: #1977980
Change-Id: I1b44921b87c98e8f98e6f308702dce9c991c12ae

fixtures/scenario004.pp

@@ -31,7 +31,7 @@ if $::operatingsystem == 'Ubuntu' {
 } else {
   $ipv6                = true
   $bgpvpn_enabled      = true
-  $l2gw_enabled        = false
+  $l2gw_enabled        = true
   $bgp_dragent_enabled = true
 }