stats/vty: Add stats configuration

This commit provides stats configuration similar to the log
configuration.

The following vty commands are added to the config node:
  stats reporter statsd          Create/Modify a statsd reporter
  no stats reporter statsd       Remove a statsd reporter

To actually configure a reporter, the config-stats node is entered
when the "stats reporter" command has succeeded. The following new
vty commands are available there:
  local-ip ADDR          Set the IP address to which we bind locally
  no local-ip            Do not bind to a certain IP address
  remote-ip ADDR         Set the remote IP address to which we connect
  remote-port <1-65535>  Set the remote port to which we connect
  prefix PREFIX          Set the item/counter name prefix
  no prefix              Do not use a prefix
  enable                 Enable the reporter
  disable                Disable the reporter

Sponsored-by: On-Waves ehf
diff --git a/include/osmocom/vty/command.h b/include/osmocom/vty/command.h
index 4eb519f..890f0d6 100644
--- a/include/osmocom/vty/command.h
+++ b/include/osmocom/vty/command.h
@@ -75,6 +75,7 @@
 	SERVICE_NODE,		/*!< \brief Service node. */
 	DEBUG_NODE,		/*!< \brief Debug node. */
 	CFG_LOG_NODE,		/*!< \brief Configure the logging */
+	CFG_STATS_NODE,		/*!< \brief Configure the statistics */
 
 	VTY_NODE,		/*!< \brief Vty node. */