diag: Correct the minimum dci packet length

Diag currently has the minuimum dci packet length set to 8. Correct
the valid minimum packet size to 5.
CRs-Fixed: 538425
Change-Id: Ie1d6becda3f1be292524051e9d6d9a7cd1f5fbe7
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>