Downgrade to 3.216 fixes it.
Here the result:
root@GL-XE300:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/root 11008 11008 0 100% /rom
tmpfs 61820 216 61604 0% /tmp
/dev/ubi0_1 102644 752 97056 1% /overlay
overlayfs:/overlay 102644 752 97056 1% /
tmpfs 512 0 512 0% /dev
/dev/sda1 3143840 912260 2231580 29% /mnt/sda1
root@GL-XE300:~# mount
/dev/root on /rom type squashfs (ro,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,noatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,noatime)
cgroup on /sys/fs/cgroup type cgroup (rw,nosuid,nodev,noexec,relatime,blkio,devices,freezer,net_cls,pids)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noatime)
/dev/ubi0_1 on /overlay type ubifs (rw,noatime,ubi=0,vol=1)
overlayfs:/overlay on / type overlay (rw,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work)
tmpfs on /dev type tmpfs (rw,nosuid,relatime,size=512k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,mode=600,ptmxmode=000)
debugfs on /sys/kernel/debug type debugfs (rw,noatime)
/dev/sda1 on /mnt/sda1 type vfat (rw,sync,relatime,fmask=0000,dmask=0000,allow_utime=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro)
root@GL-XE300:~#