staging/lustre: remove IOC_LIBCFS_PING_TEST ioctl

The ioctl IOC_LIBCFS_PING_TEST has not been used in ages.  The recent
nidstring changes which moved all the nidstring operations from libcfs
to the LNet layer but this ioctl code was still using an nidstring
operation that was causing a circular dependency loop between libcfs and
LNet.

Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>