reverse_tunnel: report initiator goaways to the reporter (#46728)

## Commit Message
reverse_tunnel: report initiator goaways to the reporter

## Description
When the initiator sends GOAWAY (listener drain or max connection
duration), the acceptor now reports that socket as gone immediately
instead of waiting for TCP close. The reporter keys tunnels by fd so a
node's replacement is not collapsed into the draining one. Before this,
unique_active stayed up until the old socket actually closed, so a
replacement tunnel looked like the same connection. GOAWAY is now
treated as the end of that fd for reporting.

## Testing
Added unit and integ tests

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Signed-off-by: aakugan <aakashganapathy2@gmail.com>