PKG_CHECK_FORMAT_SECURITY: disable it for the failing packages (for now)

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@free.fr>
Merge pull request #57 from champtar/format

PKG_CHECK_FORMAT_SECURITY: disable it for the failing packages (for now)
Merged before the changes to OpenWrt trunk in order to avoid regressions.