diag: Prevent out of bound write while sending dci pkt to remote

BugLink: https://bugs.launchpad.net/bugs/1931727



Sanitize user input length for the maximum buffer size before
writing the dci packet to remote.

Change-Id: I1f813a969fcce589f9e5024864ef4a650f2cf64e
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>
Signed-off-by: Vivek Golani <vgolani@codeaurora.org>
(cherry picked from commit 4403ee907e7f3a50a559a3b2d57bf2eeed192968)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>