Add a new topic network:network-id-changed to notify that network id is changed.

This patch splits network change event into 2 events:

1. network ID change event
   It is sent when the calculated ID differs from the previous one.

2. network change event
   It is sent when the network ID has changed or when any address has been added, removed or changed.

Backed out for wpt failures on report-only-in-meta.sub.html

Backout link: https://hg.mozilla.org/integration/autoland/rev/c04ca591730342cf46b0a9d167939242b2a1d5a2
Log link: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=273479263&repo=autoland&lineNumber=3193

I have no idea why the original patch causes the wpt failure. I tried couple of changes in the patch on try and the test fails when we send network change event when some address is modified, i.e. the same logic that was in the old code before NetlinkService was implemented https://searchfox.org/mozilla-central/rev/8afaba205627ff1b20bd6205119d301f3932cff6/netwerk/system/linux/nsNotifyAddrListener_Linux.cpp#440. I don't know why the test didn't fail with the old code. Maybe the combination of the test and platform didn't exist at that time? Anyway, I decided simply to not modify network change event and just to add the new network ID change event which is then equal to network change event on those platforms.

https://hg.mozilla.org/mozilla-central/rev/20eae859997f