[iperf3] Remove shell from the sandbox

Testing: Followed procedure in README.fuchsia
Change-Id: I25d09aa63833ccc8d6d0021a5d64ea0d0051d967
diff --git a/meta/iperf3.cmx b/meta/iperf3.cmx
index a9a4479..6eb8bbd 100644
--- a/meta/iperf3.cmx
+++ b/meta/iperf3.cmx
@@ -4,10 +4,11 @@
     },
     "sandbox": {
         "features": [
-            "shell"
+            "isolated-temp"
         ],
         "services": [
-            "fuchsia.net.SocketProvider"
+            "fuchsia.net.SocketProvider",
+            "fuchsia.posix.socket.Provider"
         ]
     }
 }