UBUNTU: [Config] linux-image-* should Suggests: linux-headers-*

To allow kernel autocleaning to work correctly we need linux-image-*
to Suggests: linux-headers-* to maintain the headers lifetime in line
with the lifetime of the kernel itself.

BugLink: http://bugs.launchpad.net/bugs/1029730
Signed-off-by: Andy Whitcroft <apw@canonical.com>