mdns: fix preset of esp_netif ptr for local interfaces
mdns: fix preset of esp_netif ptr for local interfaces

mdns module store local copy of esp_netif for common interfaces,
but it was correctly initialized only when interface started.
If the event were missed (e.g. mdns_init after interface start)
the local copy wouldn't be initialized. Fixed by restoring the local
copy.

Closes WIFI-1538

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf