LU-13004 gnilnd: discard struct kvec arg.

LU-13004 gnilnd: discard struct kvec arg.

The 'struct kvec *' are to kgnilnd_setup_rdma_buffer()
and kgnilnd_setup_immediate_buffer() is now always
NULL.  So we can remove the arg and code that handles
non-NULL values.
This means that kgnilnd_setup_virt_buffer() can
disappear completely.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ib38494693fba521a6e3dc4e6dc0cbb33dea1595b
Reviewed-on: https://review.whamcloud.com/37846
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>