MXS-2047 Rename MARIADB_GTID_INFO::file -> binlog_name

That's how the concept is named elsewhere.

server/modules/routing/binlogrouter/blr.hh

@@ -341,7 +341,7 @@ typedef struct mariadb_gtid_elems
 typedef struct mariadb_gtid_info
 {
     char               gtid[GTID_MAX_LEN + 1];      /** MariaDB 10.x GTID, string value */
-    char               file[BINLOG_FNAMELEN + 1];   /** The binlog file */
+    char               binlog_name[BINLOG_FNAMELEN + 1];   /** The binlog file */
     uint64_t           start;                       /** The BEGIN pos: i.e the GTID event */
     uint64_t           end;                         /** The next_pos in COMMIT event */
     MARIADB_GTID_ELEMS gtid_elms;                   /** MariaDB 10.x GTID components */