libupnpp: fix build with uclibc

Add patch to avoid failing with error if host_os doesn't start with
linux

Fixes:
 - http://autobuild.buildroot.net/results/cfb332a169863bcb3e6bc6ee7d6f6199f856b0b8
 - http://autobuild.buildroot.net/results/2f6f464f6360ed9ea4c238f503d2c3b8ab3cbd86



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>