net: thunderbolt: Enable full end-to-end flow control

USB4NET protocol allows the networking drivers to take advantage of
end-to-end flow control supported by the USB4 host interface. This
should prevent the receiving side from dropping network packets.

In adddition add a module parameter that can be used to turn this off
just in case it causes problems.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>