LU-12678 socklnd: convert various refcounts to refcount_t

Each of these refcounts exactly follows the expectations of
refcount_t, so change the atomic_t to refcoun_t.

We can remove the LASSERTs on incref/decref as they can now be enabled
at build time with CONFIG_REFCOUNT_FULL

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I50f13465b588c30a70568a5800619cc7ec26293d
Reviewed-on: https://review.whamcloud.com/39130
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>