glibc no longer installs libnsl.so, so there is no need to use a separate directory for the library. This means that the ldconfig bits can be removed from the application. (The compat library in glibc uses a different soname, so there isn't a file path conflict, either.)
By the way, I think you should add Conflicts: glibc-devel < glibc-2.26.9000-40 to the libnsl2-devel package, because that's the glibc version in which libnsl.so was removed.
Hi, I've fixed this in libnsl2-1.2.0-1.fc28 .