Throttle network path updates in packet tunnel

[rablador]

We should throttle the updates we receive from monitoring the default path via KVO. Since flopping back and forth can be detrimental and causes the tunnel to thrash, the changes should be throttled. Finding the optimal parameters and throttling strategy is subject to discussion.

Current implementation removes duplicate updates and throttles the remaining for 2 seconds.

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This change is 

[linear]

IOS-392 Throttle path updates in packet tunnel.

We should throttle the updates we receive from monitoring the default path via KVO. Since flopping back and forth can be detrimental and causes the tunnel to thrash, the changes should be throttled. Finding the optimal parameters and throttling strategy is subject to discussion.

Emīls: My current hunch is that we should add at least a 2 second delay to any and all path changes.

[pronebird]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[buggmagnet]

Reviewable status: complete! all files reviewed, all discussions resolved

[buggmagnet]

Reviewed 1 of 2 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved