Optionally maintain connections when IPv6 temporary addresses change

Set the flag IP_ADDRESS_CHANGE_IPV6_TEMPADDR in AddressTrackerLinux to
indicate that only IPv6 temporary addresses have changed, then check it
in TransportClientSocketPool, HttpStreamPool, SpdySessionPool, and
QuicSessionPool to determine whether to abort the connection. The
behavior is controlled by the new feature flag
kMaintainConnectionsOnIpv6TempAddrChange: If the feature flag is
disabled (the default), the old behavior of aborting all connections on
all IP address changes is preserved. If the feature flag is enabled,
only changes to IPv4 addresses or non-temporary IPv6 addresses will
abort connections.

For now, the new behavior is only available on Linux. In the future,
other platform-specific code will be modified to set
IP_ADDRESS_CHANGE_IPV6_TEMPADDR as well.

Bug: 373461934
Change-Id: I291dc58dba0de340989617f3c7b3d277f96a9c82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6847123
Reviewed-by: David Schinazi <dschinazi@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Commit-Queue: David Schinazi <dschinazi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1515025}