This updates the minimal supported version of CMake to 3.16, which in turn enables us to use more CMake features and have a cleaner build system.
This is the version that provides most new features and also the one we use in our latest docker image for CI.
Replaced hyphens with underscores in examples
project definition for all examples which had
hyphens in their project name. dpp-enrollee is
an exceptions because the name matches the
project directory name while the project
directory also contains hyphens.
esp_netif_init() returns standard esp_err_t error code (unlike tcpip_adapter init), so shall be checked for the return value
Also to make the initialization code more consistent.
inet_aton returns 0 on failure, but socket_add_ipv4_multicast_group has to return negative values for failures
getaddrinfo sets res to zero of address could not resolved, but doesn't necessarily return an
error. res is now checked for zero before dereferencing
Merges https://github.com/espressif/esp-idf/pull/2814
