libcap: add upstream xattr patch

Add upstream patch for xattr include fix.
Also rename patches to git naming convention.
Fixes:
http://autobuild.buildroot.net/results/2ef/2efb25356bc87ba0e1be08214eaa28ac064ad6c3/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>