meta-ettus-core: contrib: Set +x for build_imgs_package.sh
meta-ettus-core: contrib: Set +x for build_imgs_package.sh

If this is not set, the builds will apply the flag, leaving the tree
dirty.

Signed-off-by: Martin Braun <3d56405a74868c0c3ff5cba6e886d82741a922ab@ettus.com>

EttusResearch/meta-ettus,EttusResearch/meta-ettus,EttusResearch/meta-ettus,EttusResearch/meta-ettus,EttusResearch/meta-ettus,EttusResearch/meta-ettus