pppoe-server: bugfix MPPE node definition
pppoe-server: bugfix MPPE node definition

PPPoE server supports setting the MPPE preferences, it is implemented as node
with leafNodes for require, prefer and deny. This will render a wrong AccelPPP
configuration as it will be "None" if specified.

pppoe-server {
    ppp-options {
        mppe {
            deny
            require
        }
    }
}

instead it must be:

pppoe-server {
    ppp-options {
        mppe require
    }
}

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x