Fix ng_pppoe(4) after turning off "autosrc feature" on ng_ether(4).
- Store the Ethernet header in node softc.
- Initialize header with dst addr and ethertype in node constructor method.
- In node connect method send NGM_ETHER_GET_ENADDR message downwards.
- If received reply from ng_ether(4) store the src addr in softc.
- Add NGM_PPPOE_SETENDADDR message that allows user to override the address with whatever he/she wants.