fix(nan_console): Error when NAN Discovery is started more than once (IDFGH-13923)

[entrop1a]

Description

• Development board: ESP32-WROOM-32
• ESP-IDF version: 5.4.0

In nan_console example, when NAN is started more than once, triggers this netif error: esp_netif_lwip: esp_netif_new_api: Failed to configure netif with config=0x3ffc85e0 (config or if_key is NULL or duplicate key). This means that the existence of a created network interface was not checked.

To resolve this problem, three actions were taken:

1. Declaration of variable as null g_nan_netif;
2. Before creating the network interface, g_nan_netif is checked;
3. When NAN is stopped, g_nan_netif gets NULL.

Testing

Error log:

Fixed log:

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[nachiketkukade]

@entrop1a , thanks for your contribution, with the minor modification mentioned above, will take the PR for internal review

[entrop1a]

@nachiketkukade, thanks for your review! Modifications have been made.