Ignore parse errors from pinger when its socket is closed

[buggmagnet]

This PR fixes a race condition where we would get parse error from the pinger due to pending reads when closing its socket.

The fix is to look at whether the destAddress is still valid (i.e. socket is still open) before sending the parsing error.

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This change is 

[linear]

IOS-865 Fix race condition in TunnelPinger

[rablador]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @buggmagnet)

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ios/PacketTunnelCore/Pinger/TunnelPinger.swift line 21 at r1 (raw file):

    private let replyQueue: DispatchQueue
    private var destAddress: IPv4Address?
    // Always accessed from the `replyQueue` and is assigned once, on the main thread of the PacketTunnel. It is thread safe.

Nit: Make this comment a doc instead, with a - Note to hightlight this info.

[buggmagnet]

Reviewable status: 0 of 1 files reviewed, all discussions resolved (waiting on @rablador)

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ios/PacketTunnelCore/Pinger/TunnelPinger.swift line 21 at r1 (raw file):

Previously, rablador (Jon Petersson) wrote…

Nit: Make this comment a doc instead, with a - Note to hightlight this info.

Done

[rablador]

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

[mojganii]

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

[rablador]

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

[github-actions]

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