PADI packet contains a NULL service. This is apparently the desired
behaviour in this case, though we only allow advertising one
service. You could run multiple pppoeds to advertise multiple services.
used not to be necessary).
o Allow ``-n ngdebug'' to specify something to pass to NgSetDebug()
and redirect NgSetDebug() output to syslog(8) in daemon() mode.
o Xref ng_ether(8) and NgSetDebug(4).
o Correct the type of the response passed to NgRecvData.
