ndisc6: use LIBS for libintl

Use LIBS instead of LDFLAGS for "-lintl", otherwise LDFLAGS gets
evaluated to the left of object files and fails to link statically
because of incorrect symbol resolution order. Fixes:
http://autobuild.buildroot.net/results/21b/21bf88c9dbaecc204598e60dd9c7392a85068dd6/



Also rename patch to new naming convention.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>