LU-11986 lnet: properly cleanup lnet debugfs files

LU-11986 lnet: properly cleanup lnet debugfs files

The function lnet_router_debugfs_remove() is suppose to cleanup
the lnet specific debugfs files but that is not happening at all.
Change lnet_remove_debugfs() from doing the final debugfs lnet
and libcfs cleanup to doing specific debugfs file removal. We
can make libcfs module unloading to directly finish the entire
libcfs and debugfs tree removal instead. With this change we can
make lnet_router_debugfs_fini() call lnet_remove_debugfs().

Lustre-change: https://review.whamcloud.com/34669/
Lustre-commit: 8cb7ccf54e2d34010bea9a71fe0eff708545ab78

Change-Id: I9e314e7efde806073b621166ff2e1b344e550875
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34692
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sonia Sharma <sharmaso@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>