netgraph. Eventually we may need to have a separate hook for packets
that already have a source AMC address but for now just drop it in.
Should fix PPPoE.
This means 'options NETGRAPH' is no longer necessary in order to get
netgraph-enabled Ethernet interfaces. This supports loading/unloading
the ng_ether.ko and attaching/detaching the Ethernet interface in any
order.
Add two new hooks 'upper' and 'lower' to allow access to the protocol
demux engine and the raw device, respectively. This enables bridging
to be defined as a netgraph node, if so desired.
Reviewed by: freebsd-net@freebsd.org
