LU-9667 lnet: Generic helper functions for sysfs

LU-9667 lnet: Generic helper functions for sysfs

Adding generic helper functions for the sysfs
callback functions to use when implemented.
Add the base directory "lnet" to create the
path /sys/fs/lnet/

sysfs show and store callback functions for
lnet and lnd to use the helper functions.

Test-Parameters: trivial
Change-Id: I250eb0e3f3398f0882c2ab66dd4bf7f56871711b
Signed-off-by: Sonia Sharma <sonia.sharma@intel.com>
Reviewed-on: https://review.whamcloud.com/29163
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sonia Sharma <sharmaso@whamcloud.com>