Adjust Espressif wolfssl_echoserver example timehelper

[gojimmypi]

This PR addresses the Espressif wolfssl_echoserver build error noted in #728 when publishing wolfssh as a Managed Component by updating the example and not the library. The root cause of the problem is the un-gated header timelib functions and the respective type difference: int vs esp_err_t.

Eventually the example needs to be revised to completely remove the local timelib and use the esp-sdk-lib.h instead.

For now, since both the local example code and the esp-sdk-lib.h use the same time-related function names, the esp_err_t return type updates in this PR for the example allow an interim solution to the build problem.

Some of the other warnings observed will need to be addressed in a wolfssl update.

The REQUIRES CMake value does not need esp_netif due to the HAS_ESP_NETIF_SNTP gating in the example which is disabled by default.

Since the core wolfSSH library remains unchanged, I plan to publish the wolfSSH Espressif Managed Component with this update included on top of the v1.4.18-stable release tag.