wgengine/magicsock: add missing logf arg (#15995)

Also, add the short version of the node key in parens to match existing
patterns.

Updates #cleanup

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

wgengine/magicsock/endpoint.go

@@ -1480,7 +1480,7 @@ func (de *endpoint) addCandidateEndpoint(ep netip.AddrPort, forRxPingTxID stun.T
 			}
 		}
 		size2 := len(de.endpointState)
-		de.c.dlogf("[v1] magicsock: disco: addCandidateEndpoint pruned %v candidate set from %v to %v entries", size, size2)
+		de.c.dlogf("[v1] magicsock: disco: addCandidateEndpoint pruned %v (%s) candidate set from %v to %v entries", de.discoShort(), de.publicKey.ShortString(), size, size2)
 	}
 	return false
 }