package/ejabberd: bump to version 18.09

package/ejabberd: bump to version 18.09

This version requires much less patches than the previous one packaged
in Buildroot. It is compatible with Erlang OTP 21.
There are two remainning patches to:
- change the Makefile rules so dependencies are not downloaded/compiled;
- fix ejabberd user and load a default file in ejabberdctl script.

The patch 0006-fix-install-permissions has been replaced by setting
permissions on /etc/ejabberd directory via EJABBERD_PERMISSIONS.

The patch 0009-disable-mod_avatar has been removed because eimp is
a mandatory dependency since 0f86559d.

Signed-off-by: Johan Oudinet <johan.oudinet@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>