admin-cmd: Added smart-log command support.

This patch implements the support for smart-log command
(NVM Express 1.2.1-section 5.10.1.2 SMART / Health Information
(Log Identifier 02h)) on the target for NVMe over Fabric.

In current implementation host can retrieve following statistics:-
1. Data Units Read.
2. Data Units Written.
3. Host Read Commands.
4. Host Write Commands.

Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>