libupnp: move to version 1.6.14

As pointed by Sagaert Johan in the mailing list and further testing version
1.6.15 has some issues.
So move to version 1.6.14 which is far more stable and compliant.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>