Fix below build error:
../main/udp_client.c: In function 'udp_client_task':
../main/udp_client.c:58:41: error: 'addr_str' undeclared (first use in this function); did you mean 'caddr_t'?
Fixes: 995ef85e85 ("socket examples: add tests for server and client applications")
Signed-off-by: Axel Lin <axel.lin@gmail.com>
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.
