LU-9480 lnet: reference counts on lnet_peer/lnet_peer_net

LU-9480 lnet: reference counts on lnet_peer/lnet_peer_net

Peer discovery will be keeping track of lnet_peer structures,
so there will be references to an lnet_peer independent of
the references implied by lnet_peer_ni structures. Manage
this by adding explicit reference counts to lnet_peer_net and
lnet_peer.

Each lnet_peer_net has a hold on the lnet_peer it links to
with its lpn_peer pointer. This hold is only removed when that
pointer is assigned a new value or the lnet_peer_net is freed.
Just removing an lnet_peer_net from the lp_peer_nets list does
not release this hold, it just prevents new lookups of the
lnet_peer_net via the lnet_peer.

Each lnet_peer_ni has a hold on the lnet_peer_net it links to
with its lpni_peer_net pointer. This hold is only removed when
that pointer is assigned a new value or the lnet_peer_ni is
freed. Just removing an lnet_peer_ni from the lpn_peer_nis
list does not release this hold, it just prevents new lookups
of the lnet_peer_ni via the lnet_peer_net.

This ensures that given a lnet_peer_ni *lpni, we can rely on
lpni->lpni_peer_net->lpn_peer pointing to a valid lnet_peer.

Keep a count of the total number of lnet_peer_ni attached to
an lnet_peer in lp_nnis.

Split the global ln_peers list into per-lnet_peer_table lists.
The CPT of the peer table in which the lnet_peer is linked is
stored in lp_cpt.

Test-Parameters: trivial
Signed-off-by: Olaf Weber <olaf@sgi.com>
Change-Id: I465f9b732964834dad327fbe5177fba0cfb6775f
Reviewed-on: https://review.whamcloud.com/25784
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Amir Shehata <amir.shehata@intel.com>
Tested-by: Amir Shehata <amir.shehata@intel.com>