This commit removes the lock from the list manipulation code in esp_netif_objects.c,
because we already have another lock/task context for lwip.
So the list manipulation is unsafe and safety must be assured by the stack layer
(in esp_netif_lwip).
Problems with current locking:
* implementation of locking was wrong -- lazy init style of creating the mutex is not
thread safe (and destroying it if we have no interface makes the problem exhibit very frequently)
* locking only the list won't solve issues when assessing interfaces atomically
* maintaining multiple locks is problematic, as we often switch between
lwip context and user context in internal implementation of esp_netif_lwip
Closes https://github.com/espressif/esp-idf/issues/12261
