LU-12756 lnet: Avoid redundant peer NI lookups

LU-12756 lnet: Avoid redundant peer NI lookups

Each caller of lnet_peer_ni_traffic_add() performs a subsequent call
to lnet_peer_ni_find_locked(). We can avoid the extra lookup by having
lnet_peer_ni_traffic_add() return a peer NI pointer (or ERR_PTR as
appropriate).

lnet_peer_ni_traffic_add() now takes a ref on the peer NI to mimic
the behavior of lnet_peer_ni_find_locked().

lnet_nid2peerni_ex() only has a single caller that always passes
LNET_LOCK_EX for the cpt argument, so this function argument is
removed.

Some duplicate code dealing with ln_state handling is removed from
lnet_peerni_by_nid_locked()

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I8e9e2449ef2b958b53abd59cd2c122e5492fbb34
Reviewed-on: https://review.whamcloud.com/36623
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexey Lyashkov <alexey.lyashkov@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>