shrunk cfgobj down from 48 bytes to 40 bytes

Follow-up of 38ce2906 as the size of the `cfg_obj_t` can actually goes
down to 40 bytes "for free", by using bitfields to only use 31 bits for
the `line` field, so the remaining bit can be use to hold the `cloned`
state without paying the extra 8 bytes padding.

lib/isccfg/include/isccfg/grammar.h

@@ -206,9 +206,20 @@ struct cfg_obj {
 	 * These two 4 byte fields are contiguous to avoid an extra
 	 * padding of 4 bytes each, avoiding an extra 8 bytes in the
 	 * struct.
+	 *
+	 * `line` is 31 bits long (~2,000,000,000 is likely enough lines in a
+	 * named config) so the `cloned` boolean fit in the extra bit, and won't
+	 * take extra 8 bits because of padding.
 	 */
 	unsigned int magic;
-	unsigned int line;
+	unsigned int line : 31;
+
+	/*%
+	 * Indicates that an object was cloned from the defaults
+	 * or otherwise generated during the configuration merge
+	 * process.
+	 */
+	bool cloned : 1;
 
 	isc_refcount_t	  references;
 	cfg_obj_t	 *file; /*%< separate string with its own refcount */
@@ -226,13 +237,6 @@ struct cfg_obj {
 		cfg_netprefix_t	  *netprefix;
 		isccfg_duration_t *duration;
 	} value;
-
-	/*%
-	 * Indicates that an object was cloned from the defaults
-	 * or otherwise generated during the configuration merge
-	 * process.
-	 */
-	bool cloned;
 };
 
 /*% A list element. */

lib/isccfg/parser.c

@@ -73,8 +73,8 @@
  * can take a significant amount of memory. This assert ensures that we
  * won't increase its size by mistake without getting a warning.
  */
-static_assert(sizeof(struct cfg_obj) <= 48,
-	      "sizeof(cfg_obj_t) must be 48 bytes");
+static_assert(sizeof(struct cfg_obj) <= 40,
+	      "sizeof(cfg_obj_t) must be 40 bytes");
 
 /* Shorthand */
 #define CAT CFG_LOGCATEGORY_CONFIG