update snort to 2.9.6.0

1. looks like snort dropped reference to barnyard2. At least it's missing in configure.
Also download link to barnyard2 is not available now. Drop this package.
2. update snort version from 2.9.4.6 to 2.9.6.0.
3. fix libdnet paths.

Signed-off-by: Maxim Uvarov <maxim.uvarov@linaro.org>
Signed-off-by: Joe MacDonald <joe@deserted.net>