staging: lustre: libcfs: fix test for libcfs_ioctl_hdr minimum size

The function libcfs_ioctl_getdata() test to see if libcfs_ioctl_hdr
is smaller than struct libcfs_ioctl_data in size. This is wrong
and it breaks the ioctl that is used to collect LNet stats. The
correct size to compare against is struct libcfs_ioctl_hdr.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5935
Reviewed-on: http://review.whamcloud.com/12782


Fixes: ed2f549d ("staging: lustre: libcfs: test if userland data is to small")
Reported-by: Doug Oucharek <doug.s.oucharek@intel.com>
Reviewed-by: Liang Zhen <liang.zhen@intel.com>
Reviewed-by: Doug Oucharek <doug.s.oucharek@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>