rptun/ping: fix invalid use of nsh_error after 31421db6f

nshlib/nsh_syscmds.c

@@ -538,7 +538,7 @@ static int cmd_rptun_once(FAR struct nsh_vtbl_s *vtbl,
       if (argv[3] == 0 || argv[4] == 0 ||
           argv[5] == 0 || argv[6] == 0)
         {
-          nsh_error(vtbl, g_fmtargrequired);
+          nsh_error(vtbl, g_fmtargrequired, argv[0]);
           return ERROR;
         }