net/ip: Make struct net_addr holding uninon of ipv6/4 unconditionally

It will help to use IS_ENABLED in place of #ifdef in relevant place.

Only struct net_if uses this structure.
In case only IPv4 is used, it will bloat up this struct by 12 bytes.

There are few reasons why this is "ok" in this case:

- On limited rom/ram system it will be unlikely to find a lot of
network interfaces so it should not harm much to raise the size of
struct net_addr.
- If IPv4 is the only enabled IP version, it gains a good amount of
rom/ram to discard IPv6 support so it is fine to steal a bit of this
gain to bloat up a bit struct net_addr.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>

include/net/net_ip.h

@@ -278,12 +278,8 @@ struct sockaddr_storage {
 struct net_addr {
 	sa_family_t family;
 	union {
-#if defined(CONFIG_NET_IPV6)
 		struct in6_addr in6_addr;
-#endif
-#if defined(CONFIG_NET_IPV4)
 		struct in_addr in_addr;
-#endif
 	};
 };