Fix C++ style comment in mqtt.c
diff --git a/src/apps/mqtt/mqtt.c b/src/apps/mqtt/mqtt.c
index da70967..cd271b1 100644
--- a/src/apps/mqtt/mqtt.c
+++ b/src/apps/mqtt/mqtt.c
@@ -835,7 +835,7 @@
         if (msg_rem_len == 0) {
           /* Reset parser state */
           client->msg_idx = 0;
-          //msg_tot_len = 0;
+          /* msg_tot_len = 0; */
           fixed_hdr_idx = 0;
         }
       }