libmongo-client: upgraded to 0.1.8

Signed-off-by: Budai Laszlo <Laszlo.Budai@balabit.com>
afmongodb: Added driver id to every log message
afmongodb: Be silent when silently-drop-message is set (ON_ERROR_SILENT)

 ...otherwise... https://www.youtube.com/watch?v=qfResyFrqlM

 [ sorry :-) ]

Signed-off-by: Budai Laszlo <Laszlo.Budai@balabit.com>