diag: Respond to several mask change requests

Add support for "set all message masks" and "disable logging"
requests.

Also, avoid sending event mask update when not required. DIAG driver
propagates event mask updates, when a remote peripheral boots up.
Sometimes, the event masks are not even set yet, when a remote
peripheral comes up. In such cases, there is no need to send
mask updates.

Change-Id: I9bc83e7479e15ba7dc118f113f732a74aa0f487a
Signed-off-by: Shalabh Jain <shalabhj@codeaurora.org>