make test failed - TestUPNP_DDWRT

[zeoio]

enter make test, error message:

--- FAIL: TestUPNP_DDWRT (2.10s)
    natupnp_test.go:165: not discovered

[fjl]

Sorry, this is a known issue with this test. We can't really fix it because of a limitation with the underlying UPNP library.