Port mapper auto discovery used to run immediately after parsing the
--nat flag, giving it a slight performance boost. But this is becoming
inconvenient because we create node.Node for all geth operations
including account management and bare chain interaction. Delay
autodiscovery until the first use instead, which avoids any network
interaction until the node is actually started.
People stil get confused about the messages. This commit changes
the levels so that the only thing printed at the default level (info)
is a successful mapping.
Concurrent calls to Interface methods on autodisc could return a "not
discovered" error if the discovery did not finish before the call.
autodisc.wait expected the done channel to carry the found Interface
but it was closed instead.
The fix is to use sync.Once for now, which is easier to get right.
And there is a test. Finally.
This will have to change again when we introduce re-discovery.
I have verified that UPnP and NAT-PMP work against an older version of
the MiniUPnP daemon running on pfSense. This code is kind of hard to
test automatically.
