diag: Clear the remote address to avoid writing to stale port

Currently apps diag is not clearing the remote port address in
case peripheral subsystem restart has happened. If the remote
address is not cleared, write to a stale address may happen.

Change-Id: Idfd788d6a10c6b9b91b9d318718c0f24bb751717
Signed-off-by: Katish Paran <kparan@codeaurora.org>