libsmack: enable multi-line support for writing to load2 and change-rule

Since Linux 3.12 Smack can handle multiple rules in single write when
loading policy. Libsmack will detect this support and group rules into
blocks of PAGE_SIZE-1 bytes at most. This results in much smaller number
of syscalls and faster loading of large policy.

Signed-off-by: Rafal Krypa <r.krypa@samsung.com>
libsmack: avoid sprintf() when printing rules in long format

Signed-off-by: Rafal Krypa <r.krypa@samsung.com>