[FS#713] netifd: substantially more IFUP events are being created

[LEDE Bugs]

The following task has a new comment added:

FS#713 - netifd: substantially more IFUP events are being created
User who did this - Hans Dedecker (dedeckeh)

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Before netifd commit https://git.lede-project.org/?p=project/netifd.git;a=commitdiff;h=b8ef742bd04ebef324ae11aee56c6e1d2cb7e0ad interface update events were send without an IP address/route/data/prefix change actually happening.
This commit fixed the issue of unnecessary interface update events but as reported in https://github.com/openwrt/openwrt/issues/346 this caused a regression in the hnetd daemon implementation as it was relying on the "unnecessary" interface update events to pick up IPv6 prefix lifetime changes.
This was fixed in netifd commit https://git.lede-project.org/?p=project/netifd.git;a=commit;h=a03216660797173fbe67866f75564e3fec9c1e8d which explicitly triggers interface update events allowing the hnetd daemon to pick IPv6 prefix lifetime updates.
So reverting this commit will break hnetd daemon again or making it a controllable feature as reported in http://lists.infradead.org/pipermail/lede-dev/2017-April/007065.html is also not a clean solution.
Packages installing interface triggers are now triggered by procd when an interface parameter changes; a more sane approach would be to allow a procd interface trigger subscription for a specific interface parameter changes as most daemons are not interested in route or IPv6 prefix changes
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=713#comment2444