net/dnsfallback: add new nodes

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

net/dnsfallback/dns-fallback-servers.json

@@ -102,6 +102,27 @@
 					"HostName": "derp4b.tailscale.com",
 					"IPv4": "157.230.25.0",
 					"IPv6": "2a03:b0c0:3:e0::58f:3001"
+				},
+				{
+					"Name": "4c",
+					"RegionID": 4,
+					"HostName": "derp4c.tailscale.com",
+					"IPv4": "134.122.77.138",
+					"IPv6": "2a03:b0c0:3:d0::1501:6001"
+				},
+				{
+					"Name": "4d",
+					"RegionID": 4,
+					"HostName": "derp4d.tailscale.com",
+					"IPv4": "134.122.94.167",
+					"IPv6": "2a03:b0c0:3:d0::1501:b001"
+				},
+				{
+					"Name": "4e",
+					"RegionID": 4,
+					"HostName": "derp4e.tailscale.com",
+					"IPv4": "134.122.74.153",
+					"IPv6": "2a03:b0c0:3:d0::29:9001"
 				}
 			]
 		},