local.conf.template: bbmask opkg-collateral HYP-8849

Mask bitbake package 'opkg-collateral'. Package
meta-angstrom/recipes-angstrom/angstrom/angstrom-feed-configs.bb replaces
'opkg-collateral'. But 'bitbake world' builds both. And during rootfs
generation both packages are available. According to Murphy's law the wrong
package is installed. 'opkg-collateral' must never be built and
'opkg-collateral' ipk must not appear in the ipk installation directory.

Signed-off-by: Mario Schuknecht <mario.schuknecht@dresearch-fe.de>