attr-sql: Rename sql_attribute_t to attr_sql_provider_t

As the plugin has its origins in the sql plugin, it still uses the naming
scheme for the attribute provider implementation. Rename the class to better
match the naming scheme we use in any other plugin

src/libcharon/plugins/attr_sql/attr_sql_plugin.c

@@ -19,7 +19,7 @@
 #include <plugins/plugin_feature.h>
 
 #include "attr_sql_plugin.h"
-#include "sql_attribute.h"
+#include "attr_sql_provider.h"
 
 typedef struct private_attr_sql_plugin_t private_attr_sql_plugin_t;
 
@@ -41,7 +41,7 @@ struct private_attr_sql_plugin_t {
 	/**
 	 * configuration attributes
 	 */
-	sql_attribute_t *attribute;
+	attr_sql_provider_t *attribute;
 };
 
 METHOD(plugin_t, get_name, char*,
@@ -74,7 +74,7 @@ static bool open_database(private_attr_sql_plugin_t *this,
 			DBG1(DBG_CFG, "attr-sql plugin failed to connect to database");
 			return FALSE;
 		}
-		this->attribute = sql_attribute_create(this->db);
+		this->attribute = attr_sql_provider_create(this->db);
 		charon->attributes->add_provider(charon->attributes,
 										 &this->attribute->provider);
 	}