/usr/lib/x86_64-linux-gnu/libnsl.so is in libc6-dev 2.13-38+deb7u10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /lib/x86_64-linux-gnu/libnsl.so.1
/lib/x86_64-linux-gnu/libnsl.so.1