[reims] network - add backplane values

data/grid5000/sites/reims/network_equipments/gw-reims.json

 {
+  "backplane_bps": 128000000000,
   "channels": {
     "naming_pattern": "Po%CHANNELID%"
   },
@@ -163,7 +164,7 @@
       "rate": 1000000000
     }
   ],
-  "model": "cisco",
+  "model": "Cisco C3560E-48TD-S",
   "routes": {
 
   },

generators/input/sites/reims/net-links/gw-reims.yaml

 --- 
 gw-reims: 
-  model: cisco
+  model: Cisco C3560E-48TD-S
   kind: router
   site: reims
   snmp_community: public
@@ -11,7 +11,7 @@ gw-reims:
       addresses: 
         - 172.16.175.254
   routes: {}
-
+  backplane_bps: 128000000000,
   linecards: 
     0: 
       naming_pattern: Gi%LINECARD%/%PORT%