Update Envoy so that SNI is available

[ijsnellf]

What this PR does / why we need it:
Updates Envoy SHA so that SNI is available. SNI support was merged here: envoyproxy/envoy#3217

I am not sure about the update process for istio/proxy, so please double check this PR.

Which issue this PR fixes

Special notes for your reviewer:

Release note:

[istio-testing]

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This pull-request has been approved by: ijsnellf
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[istio-testing]

@ijsnellf: The following tests failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
prow/proxy-presubmit-asan.sh	acef8a5	link	/test proxy-presubmit-asan
prow/proxy-presubmit-tsan.sh	acef8a5	link	/test proxy-presubmit-tsan
prow/proxy-presubmit.sh	acef8a5	link	/test proxy-presubmit

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[lizan]

@rshriram if istio/istio#5715 goes to 0.8, then shouldn't this also go to 0.8?

[ijsnellf]

You are right. I'm closing this PR in favor of this one: #1757