ipfilter: Restore ipfsync

ipfsync is a WIP sync daemon designed to be used in a failover scenario.
It was removed by 5ee61c7daa511927aae8652d6a3ea78866a50ef8. This commit
restores its three files. ipfsync is in my work queue.

(cherry picked from commit 08ab34a06a9b0a84e979ff43f2d6f2d60fb37ed9)