Contribs: Update UPNP to 1.6.18

(cherry picked from commit 8dcc49ee36fc4766938afe734666e712858e2547)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

contrib/src/upnp/SHA512SUMS

-38a3459dc8ed328a72c54560c1b859941e30759a26e7359ba0a21321b02c6c7faac86338490c0b308bd7ea8a18faa5db21ce41c1e54a3362f4b5cde89bc71b2f  libupnp-1.6.17.tar.bz2
+2ce9b637a7edf544ae272aea137f735b03761a7925da0578e0073cf6429389f7f2af6cb05f666a02faa839caba3e1798ad31657afd287626b88905a5c45f3cb4  libupnp-1.6.18.tar.bz2

contrib/src/upnp/rules.mak

 # UPNP
-UPNP_VERSION := 1.6.17
+UPNP_VERSION := 1.6.18
 UPNP_URL := $(SF)/pupnp/libupnp-$(UPNP_VERSION).tar.bz2
 
 PKGS += upnp