diag: Close cmd socket after receiving remove channel

Closing of the cmd socket channel after receiving remove channel
from IPC router is dependent on restart notifier, which can cause
not closing cmd channel client when peripheral is up and channel
will keep using the old server address. The patch closes the
command channel after receiving notification from IPC router
without checking status of peripheral.

Change-Id: I0ce99550d2505731a1659ae57c6c4a166cd5cb48
Signed-off-by: Hardik Arya <harya@codeaurora.org>