Contribs: update UPNP to 1.6.15

(cherry picked from commit 3a5086c835092aa42de3aa9a43b688fd85a11e10)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/upnp/SHA512SUMS

-cd8344ba132e0dd8d6a338bfb67121f7f8b96e321bfccb5bb2a0337b618ccc65596ade110c281f31c311ff5b232f3e7e853ddcc74ea0c52c8dfdf77e42c5ca88  libupnp-1.6.14.tar.bz2
+d376adc53cf20901dcaa254813c1655f8125ee5e965e6fe3c52d45d48cb06b8a21e016a12ad7b60be0d6c8bcbc7eed0dba473389d313d140ddd073e4e77f301d  libupnp-1.6.15.tar.bz2

contrib/src/upnp/rules.mak

 # UPNP
-UPNP_VERSION := 1.6.14
+UPNP_VERSION := 1.6.15
 UPNP_URL := $(SF)/pupnp/libupnp-$(UPNP_VERSION).tar.bz2
 
 PKGS += upnp