net: qrtr: Inject BYE on remote termination

Per the QMUX protocol specification a terminating node can send a BYE
control message to signal that the link is going down, upon receiving
this all information about remote services should be discarded and local
clients should be notified.

In the event that the link was brought down abruptly the router is
supposed to act like a BYE message has arrived. As there is no harm in
receiving an extra BYE from the remote this patch implements the latter
by injecting a BYE when the link to the remote is unregistered.

The name service will receive the BYE and can implement the notification
to the local clients.

Cc: Courtney Cavin <ccavin@gmail.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>