Add missing return.

"ndp" command should deletes only neighbor cache entries, but the
  program lacks necessary "return" after the neighbor cache
  entry check, so it might deletes non neighbor cache entries.
  (it seems that usually no problem happens.)

Approved by: jkh
Reviewed by: ume

usr.sbin/ndp/ndp.c

@@ -467,6 +467,7 @@ delete(host)
 			goto delete;
 		}
 	}
+	return 0;
 delete:
 	if (sdl->sdl_family != AF_LINK) {
 		printf("cannot locate %s\n", host);