[servan/fpga] add rate to fix mkmotd on grenoble and fix dhcp bind filed

data/grid5000/sites/grenoble/clusters/servan/nodes/servan-1.json

@@ -286,6 +286,7 @@
       "mountable": true,
       "mounted": false,
       "network_address": "servan-1-fpga0.grenoble.grid5000.fr",
+      "rate": 25000000000,
       "switch": "gw",
       "switch_port": "ethernet1/1/97"
     },
@@ -301,6 +302,7 @@
       "mountable": true,
       "mounted": false,
       "network_address": "servan-1-fpga1.grenoble.grid5000.fr",
+      "rate": 25000000000,
       "switch": "gw",
       "switch_port": "ethernet1/1/98"
     }