[WIP] automatically set GNRC_NETIF_NUMOF

[benpicco]

Contribution description

Currently, GNRC_NETIF_NUMOF has to be set manually.
This PR changes that so that each network interface will increment GNRC_NETIF_NUMOF at compile-time.

Since GNRC_NETIF_NUMOF now consists of 0 + 0 + sizeof(…) + 0 + sizeof(…) + … the processor can not evaluate it anymore. This is not a problem since the compiler will see the same job if it sees an if (0).
But as a prerequisite, many #if (GNRC_NETIF_NUMOF > 0) had to be changed into if (GNRC_NETIF_NUMOF > 0).

As expected, code size did not increase.

Testing procedure

Check if everything still works, especially examples/tests that define GNRC_NETIF_NUMOF := 2

Issues/PRs references

#11979
#9903

[gschorcht]

What about modules esp_now, esp_wifi and esp_eth? All of them provide a separate netif.

[benpicco]

Will add those!
Why are they not initialized in sys/auto_init/netif/?

[gschorcht]

The initialization of these netdevs is called as for other drivers in sys/auto_init/auto_init.c

RIOT/sys/auto_init/auto_init.c

Lines 244 to 259 in 3779635

	#ifdef MODULE_ESP_ETH
	extern void auto_init_esp_eth(void);
	auto_init_esp_eth();
	#endif
	/* don't change the order of auto_init_esp_now and auto_init_esp_wifi */
	#ifdef MODULE_ESP_NOW
	extern void auto_init_esp_now(void);
	auto_init_esp_now();
	#endif
	/* don't change the order of auto_init_esp_now and auto_init_esp_wifi */
	#ifdef MODULE_ESP_WIFI
	extern void auto_init_esp_wifi(void);
	auto_init_esp_wifi();
	#endif

The difference is, that the implementations of the auto_init_* functions are not placed in separate files in sys/auto_init/netif but in cpu/esp*/esp_*/esp_*_netdev.c. The reason is that these netdevs are platform specific and shouldn't be placed in a common place.

[benpicco]

I see! But stm32_eth and nrf802154 are platform specific too…

[gschorcht]

Yes. The question is whether we should move the auto_init_esp_* code to sys/auto_init/netif or whether we should leave it as it is.

[leandrolanzieri]

What about defining a generic NETIF_NUMOF here and make GNRC use that? so we could keep this stack agnostic