wgengine/magicsock: only log about lazy config when actually doing lazy config.

Before, tailscaled would log every 10 seconds when the periodic noteRecvActivity
call happens. This is noisy, but worse it's misleading, because the message
suggests that the disco code is starting a lazy config run for a missing peer,
whereas in fact it's just an internal piece of keepalive logic.

With this change, we still log when going from 0->1 tunnel for the peer, but
not every 10s thereafter.

Signed-off-by: David Anderson <danderson@tailscale.com>

wgengine/magicsock/magicsock.go

@@ -1878,9 +1878,7 @@ func (c *Conn) handleDiscoMessage(msg []byte, src netaddr.IPPort) bool {
 		// it's an idle endpoint that doesn't yet exist in the wireguard config. We now have
 		// to notify the userspace engine (via noteRecvActivity) so wireguard-go can create
 		// an Endpoint (ultimately calling our CreateEndpoint).
-		if debugDisco {
-			c.logf("magicsock: disco: got message from inactive peer %v", sender.ShortString())
-		}
+		c.logf("magicsock: got disco message from idle peer, starting lazy conf for %v, %v", peerNode.Key.ShortString(), sender.ShortString())
 		if c.noteRecvActivity == nil {
 			c.logf("magicsock: [unexpected] have node without endpoint, without c.noteRecvActivity hook")
 			return false
@@ -1890,7 +1888,6 @@ func (c *Conn) handleDiscoMessage(msg []byte, src netaddr.IPPort) bool {
 		needsRecvActivityCall = de.isFirstRecvActivityInAwhile()
 	}
 	if needsRecvActivityCall && c.noteRecvActivity != nil {
-		c.logf("magicsock: got disco message from idle peer, starting lazy conf for %v, %v", peerNode.Key.ShortString(), sender.ShortString())
 		// We can't hold Conn.mu while calling noteRecvActivity.
 		// noteRecvActivity acquires userspaceEngine.wgLock (and per our
 		// lock ordering rules: wgLock must come first), and also calls