[Feature Request] Add support for filtering syslog packets using same mechanism as Netflow

[ASchneider-GitHub]

Currently Ktranslate supports filtering via packet attributes when ingesting Netflow, which is described here: https://docs.newrelic.com/docs/network-performance-monitoring/advanced/advanced-config/#flow-data-input-filtering. As an example, you can ignore all packets that are not on a specific port:

-nf.source netflow5 --filters int,l4_dst_port,!=,8531

Since Syslog packets also contain fields that can be used in the same way as documented above, it would be nice if Ktranslate could apply the same --filter mechanism toward them as well.