LU-12678 o2iblnd: convert ibp_refcount to a kref

LU-12678 o2iblnd: convert ibp_refcount to a kref

This refcount is used exactly like a kref.  So change it to one.
kref uses refcount_t which will warn on increment-from-zero and
similar problems (which enabled with CONFIG option), so we don't
need the LASSERT calls.

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: James Simmons <jsimmons@infradead.org>
Change-Id: I23ade8c2f768c70a1fd330e8c173e0d18f5ff976
Reviewed-on: https://review.whamcloud.com/45685
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>