Missing GPL Source for ReadyNAS 6.8.1

with  GPL for 6.9.0

http://www.readynas.com/contributed/mdgm/tmp/ReadyNASOS_V6.9.0_WW_src.zip

The build failed..

 LD fs/case/built-in.o
 CC fs/cifs/cifsfs.o
 CC fs/cifs/cifssmb.o
 CC fs/cifs/cifs_debug.o
 CC fs/cifs/connect.o

In file included from include/linux/kernel.h:13:0,
                 from include/linux/list.h:8,
                 from include/linux/wait.h:6,
                 from include/linux/fs.h:5,
                 from fs/cifs/connect.c:21:
fs/cifs/connect.c: In function ‘server_unresponsive’:
fs/cifs/connect.c:510:34: error: ‘struct TCP_Server_Info’ has no member named ‘echo_interval’
     server->hostname, (2 * server->echo_interval) / HZ);
                                  ^
include/linux/printk.h:410:50: note: in definition of macro ‘pr_debug_ratelimited’
   __dynamic_pr_debug(&descriptor, pr_fmt(fmt), ##__VA_ARGS__); \
                                                  ^
fs/cifs/connect.c:509:3: note: in expansion of macro ‘cifs_dbg’
   cifs_dbg(VFS, "Server %s has not responded in %lu seconds. Reconnecting...\n",
   ^
In file included from fs/cifs/connect.c:49:0:
fs/cifs/connect.c:510:34: error: ‘struct TCP_Server_Info’ has no member named ‘echo_interval’
     server->hostname, (2 * server->echo_interval) / HZ);
                                  ^
fs/cifs/cifs_debug.h:58:23: note: in definition of macro ‘cifs_dbg’
   cifs_vfs_err(fmt, ##__VA_ARGS__);   \
                       ^
In file included from include/linux/kernel.h:13:0,
                 from include/linux/list.h:8,
                 from include/linux/wait.h:6,
                 from include/linux/fs.h:5,
                 from fs/cifs/connect.c:21:
fs/cifs/connect.c:510:34: error: ‘struct TCP_Server_Info’ has no member named ‘echo_interval’
     server->hostname, (2 * server->echo_interval) / HZ);
                                  ^
include/linux/printk.h:410:50: note: in definition of macro ‘pr_debug_ratelimited’
   __dynamic_pr_debug(&descriptor, pr_fmt(fmt), ##__VA_ARGS__); \
                                                  ^
fs/cifs/connect.c:509:3: note: in expansion of macro ‘cifs_dbg’
   cifs_dbg(VFS, "Server %s has not responded in %lu seconds. Reconnecting...\n",
   ^
scripts/Makefile.build:258: recipe for target 'fs/cifs/connect.o' failed
make[2]: *** [fs/cifs/connect.o] Error 1
scripts/Makefile.build:403: recipe for target 'fs/cifs' failed
make[1]: *** [fs/cifs] Error 2
Makefile:964: recipe for target 'fs' failed
make: *** [fs] Error 2