The packetsocket link endpoint is used to enable a packet endpoint to
receive packets right before they are sent to the driver for outgoing
packets or right after they are recieved from the driver for incoming
packets.
Before this change, only packets that are sent/received by the
`stack.nic` were delivered to packet endpoints. However, the packet
endpoint should also receive packets that don't reach `stack.nic`.
Such an example can be when the interface is bridged and an incoming
packet is sent out through a sibling bridge port instead of being
delivered to a `stack.nic`.
The packetsocket link endpoint must wrap a link endpoint that
populates the link headers for ingress packets. It should ideally
be placed as low in the link endpoint heirarchy as possible so that
packets are probed as close to device drivers as possible.
https://github.com/google/gvisor/commit/2d9b33c0fd7d812a7296cd71f14c03925f815f28
removed the original packetsocket link endpoint which only allowed
low-level capturing of outbound packets but not inbound packets.
The CL mentioned above is cl/395761629.
PiperOrigin-RevId: 424947620
This change removes NetworkDispatcher.DeliverOutboundPacket.
Since all packet writes go through the NIC (the only NetworkDispatcher),
we can deliver outgoing packets to interested packet endpoints before
writing the packet to the link endpoint as the stack expects that all
packets that get delivered to a link endpoint are transmitted on the
wire. That is, link endpoints no longer need to let the stack know when
it writes a packet as the stack already knows about the packet it writes
through a link endpoint.
PiperOrigin-RevId: 395761629
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