posix: netdb: ensure that EAI constants are defined
Constants like `EAI_SYSTEM` should be defined in `<netdb.h>`
according to the spec.
In Zephyr, they should be defined via appropriately
namespaced z-variants (currently `DNS_EAI_SYSTEM` and so on).
#include <zephyr/net/socket.h>
+#define EAI_BADFLAGS DNS_EAI_BADFLAGS
+#define EAI_NONAME DNS_EAI_NONAME
+#define EAI_AGAIN DNS_EAI_AGAIN
+#define EAI_FAIL DNS_EAI_FAIL
+#define EAI_NODATA DNS_EAI_NODATA
+#define EAI_MEMORY DNS_EAI_MEMORY
+#define EAI_SYSTEM DNS_EAI_SYSTEM
+#define EAI_SERVICE DNS_EAI_SERVICE
+#define EAI_SOCKTYPE DNS_EAI_SOCKTYPE
+#define EAI_FAMILY DNS_EAI_FAMILY
+#define EAI_OVERFLOW DNS_EAI_OVERFLOW
+
#ifdef __cplusplus
extern "C" {
#endif
