kbuild, deb-pkg: fix Section field

Section "base" has been removed, the base is defined by Priority field.

For Squeeze the section should be "kernel", but as that's not yet
supported for Sarge and Etch we stay with admin for now.

Signed-off-by: maximilian attems <max@stro.at>
Signed-off-by: Frans Pop <elendil@planet.nl>
Cc: Andres Salomon <dilinger@debian.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>