LU-10391 lnet: discard some peer_ni lookup functions

lnet_nid2peerni_locked(), lnet_peer_get_ni_locked(),
lnet_find_peer4(), and lnet_find_peer_ni_locked() each have few users
left and that can call be change to use alternate versions which take
'struct lnet_nid' rather than 'lnet_nid_t'.

So convert all those callers over, and discard the older functions.

Test-Parameters: trivial testlist=sanity-lnet
Test-Parameters: serverversion=2.12 serverdistro=el7.9 testlist=runtests
Test-Parameters: clientversion=2.12 testlist=runtests
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I9f0ebd0631c2e4160c3198aa37f16b45027bce3d
Reviewed-on: https://review.whamcloud.com/44624
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>