crypto/tls: 500% increase in allocations from `(*tls.Conn).Read` in go 1.17 [1.17 backport]

[gopherbot]

@dt requested issue #50657 to be considered for backport to the next 1.17 minor release.

I'm unclear as to whether or not the performance regression seen here qualifies for a backport under the backport policy's definition of a serious issue with no workaround:

A “serious” problem is one that prevents a program from working at all.

I'll go ahead and open backport issues to continue the discussion there I guess?

@gopherbot please consider this for backport to 1.17, as it is a regression compared to 1.16.

@gopherbot please consider this for backport to 1.18, as it is a regression compared to 1.16.

[heschi]

This is a significant performance regression with what looks like a small fix. Assuming the backport is similarly small, approved.

[gopherbot]

Change https://go.dev/cl/405544 mentions this issue: crypto/tls: avoid extra allocations in steady-state Handshake calls

[heschi]

cc @golang/security to review the fix

[gopherbot]

Closed by merging 03c2e56 to release-branch.go1.17.