package/libupnp18: bump to version 1.8.6

package/libupnp18: bump to version 1.8.6

This version fixes a runtime issue which crashes gerbera:
https://github.com/gerbera/gerbera/issues/522

The issue has been reported upstream:
https://github.com/mrjimenez/pupnp/pull/122

The fix for this issue is the only "useful" commit between 1.8.5 and
1.8.6:

$ git --no-pager log --format=oneline release-1.8.5..release-1.8.6
71a47673795e9228775959ea23a984ff6c4d0a43 (tag: release-1.8.6) Adjust the library numbers for release
436aae7b617a4cd7bc1e1411d6882780699eb2ee Put the 1.8.6 release on README.md
90069231d83d2f365b76e2b15d918dfb06209970 Update README.md
7d6158d2c88245f2da4354a8bd0bc359eb15fac6 Update Changelog and THANKS
463f1cc025b27af35b0b73a05ba379d0051bcedf Fix format string for ExtraHeaders
8516da470bf32fa1f5c6f59aac3508378d5a85be Homekeeping for the next release

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>