Add comments for MDNS code

ports/espressif/common-hal/mdns/Server.c

@@ -33,14 +33,19 @@
 
 #include "components/mdns/include/mdns.h"
 
-STATIC bool inited = false;
+// Track whether the underlying IDF mdns has been started so that we only
+// create a single inited MDNS object to CircuitPython. (After deinit, another
+// could be created.)
+STATIC bool mdns_started = false;
 
 void mdns_server_construct(mdns_server_obj_t *self, bool workflow) {
-    if (inited) {
+    if (mdns_started) {
+        // Mark this object as deinited because another is already using MDNS.
         self->inited = false;
         return;
     }
     mdns_init();
+    mdns_started = true;
 
     uint8_t mac[6];
     esp_netif_get_mac(common_hal_wifi_radio_obj.netif, mac);
@@ -81,7 +86,7 @@ void common_hal_mdns_server_deinit(mdns_server_obj_t *self) {
         return;
     }
     self->inited = false;
-    inited = false;
+    mdns_started = false;
     mdns_free();
 }
 

ports/espressif/common-hal/mdns/Server.h

@@ -32,7 +32,7 @@ typedef struct {
     mp_obj_base_t base;
     const char *hostname;
     const char *instance_name;
-    // "cpy-" "XXXXXX" "\0"
-    char default_hostname[4 + 6 + 1];
+    char default_hostname[sizeof("cpy-XXXXXX")];
+    // Track if this object owns access to the underlying MDNS service.
     bool inited;
 } mdns_server_obj_t;

ports/raspberrypi/common-hal/mdns/Server.c

@@ -48,6 +48,7 @@ STATIC bool object_inited = false;
 
 void mdns_server_construct(mdns_server_obj_t *self, bool workflow) {
     if (object_inited) {
+        // Mark the object as deinit since another is already using MDNS.
         self->inited = false;
         return;
     }

ports/raspberrypi/common-hal/mdns/Server.h

@@ -34,8 +34,8 @@ typedef struct {
     mp_obj_base_t base;
     const char *hostname;
     const char *instance_name;
-    // "cpy-" "XXXXXX" "\0"
-    char default_hostname[4 + 6 + 1];
+    char default_hostname[sizeof("cpy-XXXXXX")];
     const char *service_type[MDNS_MAX_SERVICES];
+    // Track if this object owns access to the underlying MDNS service.
     bool inited;
 } mdns_server_obj_t;