net/icmp: Eliminate a warning.

net/icmp/icmp_input.c

@@ -2,7 +2,8 @@
  * net/icmp/icmp_input.c
  * Handling incoming ICMP input
  *
- *   Copyright (C) 2007-2009, 2012, 2014-2015 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2007-2009, 2012, 2014-2015, 2017 Gregory Nutt. All rights
+ *     reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Adapted for NuttX from logic in uIP which also has a BSD-like license:
@@ -333,11 +334,15 @@ void icmp_input(FAR struct net_driver_s *dev)
   return;
 
 typeerr:
+
 #ifdef CONFIG_NET_STATISTICS
   g_netstats.icmp.typeerr++;
 #endif
 
+#ifdef CONFIG_NET_ICMP_SOCKET
 drop:
+#endif
+
 #ifdef CONFIG_NET_STATISTICS
   g_netstats.icmp.drop++;
 #endif