zebra: close the incoming channel
zebra: close the incoming channel

In general the writer should close the channel, thus we can close the channel here directly.
If zebra has disconnected the `closeChannel` method will in most cases not even close the channel
because no more messages can be received on it.
fujita/gobgp,osrg/gobgp,osrg/gobgp,a16/gobgp,a16/gobgp,a16/gobgp,osrg/gobgp,fujita/gobgp,a16/gobgp,osrg/gobgp,fujita/gobgp,fujita/gobgp,a16/gobgp,a16/gobgp,a16/gobgp