wgengine/magicsock: fix debug disco printing of alloc resp disco keys (#17087)

Updates tailscale/corp#30818

Signed-off-by: Jordan Whited <jordan@tailscale.com>

wgengine/magicsock/magicsock.go

@@ -2411,11 +2411,11 @@ func (c *Conn) handleDiscoMessage(msg []byte, src epAddr, shouldBeRelayHandshake
 				msgType, sender.ShortString(), derpNodeSrc.ShortString())
 			return
 		} else {
-			c.dlogf("[v1] magicsock: disco: %v<-%v (%v, %v) got %s, for %d<->%d",
+			c.dlogf("[v1] magicsock: disco: %v<-%v (%v, %v) got %s for %v<->%v",
 				c.discoShort, epDisco.short,
 				ep.publicKey.ShortString(), derpStr(src.String()),
 				msgType,
-				req.ClientDisco[0], req.ClientDisco[1])
+				req.ClientDisco[0].ShortString(), req.ClientDisco[1].ShortString())
 		}
 
 		if c.filt == nil {