syslog-ng: update to version 3.26.1

- Bump version also in the config file
- Move logread to /sbin location instead of /usr/sbin
Because package logd in OpenWrt's ubox Makefile uses /sbin folder and LuCI has
the same path hardcoded in
modules/luci-base/root/usr/share/rpcd/acl.d/luci-base.json and using
different location results that LuCI is not able to load log data as it
is not found.

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
(cherry picked from commit fe165eeb)