utils: apply access rules to load/load2 in one shot

Open load/load2 before calling `nftw()`. Inside the callback only
collect rules using `smack_accessed_add_from_file()`. Finally, after
returning from `nftw()`, call `smack_accesses_save()` or
`smack_accesses_clear()`. This was inspired by ideas and feedback
from Rafal Krypa <r.krypa@samsung.com>.