pstats: Set default value for `pstats-max-queue-size` to 4

Otherwise any multithreaded application is dropping frames like mad, since the packets for different frames may be added to the same queue at roughly the same time.

panda/src/pstatclient/config_pstatclient.cxx

@@ -43,7 +43,7 @@ ConfigVariableBool pstats_threaded_write
           "broken with the threaded network interfaces."));
 
 ConfigVariableInt pstats_max_queue_size
-("pstats-max-queue-size", 1,
+("pstats-max-queue-size", 4,
  PRC_DESC("If pstats-threaded-write is true, this specifies the maximum "
           "number of packets (generally, frames of data) that may be queued "
           "up for the thread to process.  If this is large, the writer "