net: if: Fix array comparison warning

This commit fixes the array comparison warning (`-Warray-compare`) on
the `_net_if_list_start` and `_net_if_list_end` arrays by making the
comparison explicitly on the addresses rather than the array itself.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: stephanosio

subsys/net/ip/net_if.c

@@ -563,7 +563,7 @@ struct net_if *net_if_get_default(void)
 {
 	struct net_if *iface = NULL;
 
-	if (_net_if_list_start == _net_if_list_end) {
+	if (&_net_if_list_start[0] == &_net_if_list_end[0]) {
 		return NULL;
 	}