Add #include <string.h> in snmp_netconn.c because memset() is used
diff --git a/src/apps/snmp/snmp_netconn.c b/src/apps/snmp/snmp_netconn.c
index 27c004d..24c3e26 100644
--- a/src/apps/snmp/snmp_netconn.c
+++ b/src/apps/snmp/snmp_netconn.c
@@ -36,6 +36,7 @@
 
 #if LWIP_SNMP && SNMP_USE_NETCONN
 
+#include <string.h>
 #include "lwip/api.h"
 #include "lwip/ip.h"
 #include "lwip/udp.h"