basic: include only what we use

This is a cleaned up result of running iwyu but without forward
declarations on src/basic.

src/basic/ether-addr-util.c

@@ -19,7 +19,9 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include <net/ethernet.h>
 #include <stdio.h>
+#include <sys/types.h>
 
 #include "ether-addr-util.h"
 #include "macro.h"