LU-10391 lnet: extend nids in struct lnet_msg

LU-10391 lnet: extend nids in struct lnet_msg

struct lnet_msg contains 3 nids and one process_id (which itself
contains a nid.  Replace each of these with the 'struct lnet_nid'
version.

Test-Parameters: trivial
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: Ic6233d36bafda364894d89b2e2b055538a6033f5
Reviewed-on: https://review.whamcloud.com/43598
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>