exporters: Compute Suricata SIDs by a hash

exporters: Compute Suricata SIDs by a hash

This function is not perfect, but substantially faster when writing out
the list. We will have some somewhat-stable hash here which will always
return the same result per domain unless there has already been a small
collision.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>