PVLV: reset urgency when VS gates

[garymm]

In BOA, urgency is a mechanism to encourage gating by exciting the VsMtxGo layer. It doesn't make sense to maintain the same level of urgency once gating occurs.

Change-Id: Icb61e1d1515f5a382ec239eff2ff517c8dcf5fc5

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +0.07 :tada:

Comparison is base (9583285) 30.10% compared to head (e3a63e2) 30.18%.

:exclamation: Current head e3a63e2 differs from pull request most recent head 0138d64. Consider uploading reports for the commit 0138d64 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #271 +/- ## ========================================== + Coverage 30.10% 30.18% +0.07% ========================================== Files 85 80 -5 Lines 15281 15251 -30 ========================================== + Hits 4601 4603 +2 + Misses 10420 10386 -34 - Partials 260 262 +2 ``` | [Impacted Files](https://app.codecov.io/gh/emer/axon/pull/271?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=emer) | Coverage Δ | | |---|---|---| | [axon/pvlv.go](https://app.codecov.io/gh/emer/axon/pull/271?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=emer#diff-YXhvbi9wdmx2Lmdv) | `54.23% <0.00%> (-0.31%)` | :arrow_down: | ... and [13 files with indirect coverage changes](https://app.codecov.io/gh/emer/axon/pull/271/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=emer)

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[rcoreilly]

do we want to update and merge this in time for 1.8.5? I have a small window here where I'm online today..

[garymm]

I can merge it if / when I'm confident it helps.

[etuleu]

The results look good with this change, so I think we should merge it in and make a release. But I also had to popcode the Dist and Terrain layers.