staging: lustre: lustre: ptlrpc: sec.c: Replacing strncat with strlcat to avoid overwrite size

Changed from using strncat with strlcat to avoid overwrite the max size.
Take the opportunity to change a snprint to strlcpy.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Acked-by: Chen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>