cdc-acm: add sanity checks

[ Upstream commit 7e860a6e7aa62b337a61110430cd633db5b0d2dd ]

Check the special CDC headers for a plausible minimum length.
Another big operating systems ignores such garbage.

Change-Id: I0239f39e4f6cedbf77c049f6c72cadb78009db94
Signed-off-by: Oliver Neukum <oneukum@suse.de>
CC: stable@vger.kernel.org
Reviewed-by: Adam Lee <adam8157@gmail.com>
Tested-by: Adam Lee <adam8157@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>