extmod/modnetwork: Forward if.config(hostname) to network.hostname.

This removes the duplicate code in cyw43, esp32, esp8266 that implements
the same logic as network.hostname.

Renames the `mod_network_hostname` (where we store the hostname value in
`.data`) to `mod_network_hostname_data` to make way for calling the shared
function `mod_network_hostname`.

And uses memcpy for mod_network_hostname_data, because the length of source
is already known and removes reliance on string data being null-terminated.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

ports/mimxrt/cyw43_configport.h

@@ -61,7 +61,7 @@
 #define CYW43_THREAD_EXIT               MICROPY_PY_LWIP_EXIT
 #define CYW43_THREAD_LOCK_CHECK
 
-#define CYW43_HOST_NAME                 mod_network_hostname
+#define CYW43_HOST_NAME                 mod_network_hostname_data
 
 #define CYW43_SDPCM_SEND_COMMON_WAIT    __WFI();
 #define CYW43_DO_IOCTL_WAIT             __WFI();