LU-16213 kfilnd: Rename struct kfilnd_peer members

LU-16213 kfilnd: Rename struct kfilnd_peer members

Prefix members of struct kfilnd_peer with kp_ to make these variable
names easier to find.

Also use 'kp' as a standard name for pointers to struct kfilnd_peer
instead of 'peer' (again to make these pointers easier to find). As
such, struct kfilnd_transaction::peer is also renamed to
struct kfilnd_transaction::tn_kp.

HPE-bug-id: LUS-11128
Test-Parameters: trivial
Change-Id: Id535c7af28a5335026037a55920c706a4e16f947
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48780
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ron Gredvig <ron.gredvig@hpe.com>
Reviewed-by: Ian Ziemba <ian.ziemba@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>