wgengine/magicsock: remove some log spam

Fixes tailscale/corp#3070

Change-Id: Ie50031800ec8669e0596ad6d59d1e329a5c88516
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/magicsock/magicsock.go

@@ -2319,6 +2319,7 @@ func (c *Conn) SetNetworkMap(nm *netmap.NetworkMap) {
 		}
 		ep.wgEndpoint = n.Key.UntypedHexString()
 		ep.initFakeUDPAddr()
+		if debugDisco { // rather than making a new knob
 			c.logf("magicsock: created endpoint key=%s: disco=%s; %v", n.Key.ShortString(), n.DiscoKey.ShortString(), logger.ArgWriter(func(w *bufio.Writer) {
 				const derpPrefix = "127.3.3.40:"
 				if strings.HasPrefix(n.DERP, derpPrefix) {
@@ -2342,6 +2343,7 @@ func (c *Conn) SetNetworkMap(nm *netmap.NetworkMap) {
 					fmt.Fprintf(w, "ep=%v ", ep)
 				}
 			}))
+		}
 		ep.updateFromNode(n)
 		c.peerMap.upsertEndpoint(ep, key.DiscoPublic{})
 	}