Adds new Uplink session interface, the corresponding client side (Client,
Connection), and the corresponding API archives. An Uplink session is almost
the same as a NIC session with the difference that the roles of the end points
are swapped. An Uplink client is the one that provides a network interface
(for instance, a NIC driver) whereas an Uplink server is the one that uses
that network interface (for instance, a networking stack).
Therefore, in contrast to the NIC session, MAC address and link state come from
the Uplink client. The link state is reflected through the lifetime of an
Uplink session: The client requests the session only when the link state is
"UP" and closes it whenever the link state becomes "DOWN" again. The MAC
address is transmitted from the Uplink client to the Uplink server as an
argument of the session request.
Ref #3961
