If the peer requests a MRU option, set the mtu for the network
phase. When we are in link establishment phase, we should
continue to behave as if no option has been set and the peer
should use the default MRU.
This option is required for the Huawei E160G modem.
There are only about 4 protocols that the current ppp code handles and
it is doubtful that it will grow much more. There's no point in having
an extensive packet handler registration framework.
The connect callback was not giving enough information and the
information it was providing was not in a convenient form.
- Provide the ppp interface name (e.g. tun0)
- Provide ip, dns1 & dns2 as strings
- Do not send the ppp structure in the callback, it is most likely
present in the user data anyway