Idea was from ad6c6361f9 ("ath79: enable all space on Netgear ar9344-based WNDR routers")
These stock partitons: "backup", "hw_panic", "overly", firmware_backup", "opt"
do not contain any device-specific data and can be used for /overlay, resulting in
121M space
Users should erase those partitions with command `mtd erase <partition name>` prior to
upgrading to this version
Signed-off-by: DENG Qingfang <dengqf6@mail2.sysu.edu.cn>
5829672a9a