New param hashing spec

- When listing all params, lead with _HASH_CHECK value for cache load
 - When set value on _HASH_CHECK is rx'd, stop any ongoing listing req

src/modules/systemlib/param/param.c

@@ -1121,7 +1121,7 @@ uint32_t param_hash_check(void)
 		const char *name = param_name(param);
 		const void *val = param_get_value_ptr(param);
 		param_hash = crc32part((const uint8_t *)name, strlen(name), param_hash);
-		param_hash = crc32part(val, sizeof(union param_value_u), param_hash);
+		param_hash = crc32part(val, param_size(param), param_hash);
 	}
 
 	param_unlock();

src/modules/systemlib/param/param.h

@@ -82,6 +82,11 @@ typedef uintptr_t	param_t;
  */
 #define PARAM_INVALID	((uintptr_t)0xffffffff)
 
+/**
+ * Magic handle for hash check param
+ */
+#define PARAM_HASH      ((uintptr_t)INT32_MAX)
+
 /**
  * Look up a parameter by name.
  *