Fixed discovering of modules on 64-bit big-endian systems.

The nxt_conf_map_object() function used nxt_int_t for NXT_CONF_MAP_INT, which
was 8 bytes long on 64-bit systems.

But the nxt_port_main_start_worker_handler() used it to map into the int field
of the nxt_common_app_conf_t structure, which was 4 bytes.  As the result, on
a 64-bit big-endian system all the meaningful module type numbers were assigned
into the gap above the "type" field.

The bug was discovered on IBM/S390x.

src/nxt_conf.c

@@ -525,7 +525,7 @@ nxt_conf_map_object(nxt_mp_t *mp, nxt_conf_value_t *value, nxt_conf_map_t *map,
         uint8_t     ui8;
         int32_t     i32;
         int64_t     i64;
-        nxt_int_t   i;
+        int         i;
         ssize_t     size;
         off_t       off;
         nxt_msec_t  msec;