Move recv timer to start before crossbream receiver recv_timeout() (#642)

The timer starting after recv_timeout() means the measured time will NOT
include time spent waiting for the first PacketBatch from the receiver.

streamer/src/streamer.rs

@@ -361,9 +361,9 @@ fn recv_send(
 pub fn recv_packet_batches(
     recvr: &PacketBatchReceiver,
 ) -> Result<(Vec<PacketBatch>, usize, Duration)> {
+    let recv_start = Instant::now();
     let timer = Duration::new(1, 0);
     let packet_batch = recvr.recv_timeout(timer)?;
-    let recv_start = Instant::now();
     trace!("got packets");
     let mut num_packets = packet_batch.len();
     let mut packet_batches = vec![packet_batch];