LU-14390 gnilnd: Use DIV_ROUND_UP to calculate niov

LU-14390 gnilnd: Use DIV_ROUND_UP to calculate niov

Use DIV_ROUND_UP to calculate niov, also remove 'unlikely'
as this is the common case.

Fixes: 7a74d382 ("LU-13004 modules: replace lnet_kiov_t with struct bio_vec")
Test-Parameters: trivial
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: Iaf62326743ebe5e92bb3aa4b5780b47a5cfdfb18
Reviewed-on: https://review.whamcloud.com/41371
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>