diag: Add IOCTL support to query ODL session PID

Add IOCTL support to respond with pid of an active ODL session when
queried by ODL application.

Change-Id: I20216c7e3f98455f1d871b7a88ad99505a98db78
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>