diag: Clearing the mask before switching logging mode

Currently there is a possibility of not clearing a mask
when logging mode is switched via ioctl. The patch adds
clearing of mask before switching logging mode from ioctl.

CRs-Fixed: 2206931
Change-Id: Iaff41e67c963b2333be0cf5853ad657764a71cc1
Signed-off-by: Hardik Arya <harya@codeaurora.org>