LU-15595 lnet: LNet peer aliveness broken

LU-15595 lnet: LNet peer aliveness broken

The peer health feature used on LNet routers is intended to detect if
a peer is dead or alive by keeping track of the last time it received
a message from the peer. If the last alive value is outside of a
configurable interval then the peer is considered dead and the router
will drop messages to that peer rather than attempt to send to it.

This feature no longer works as intended because even if the
last alive value is outside the interval the router will still
consider the peer NI to be alive if the health value of the NI and
the cached status both indicate the peer NI is alive.

So even if a router has not received any messages from the client in
days, as long as the router thinks the peer's interfaces are healthy
then it will consider the peer alive. This doesn't make any sense as
peers are supposed to regularly ping the router, and if they don't do
so then they should not be considered alive.

Fix the issue by relying solely on the last alive value to determine
peer aliveness. Do not consider the health value or cached status
when determining whether to drop the message.

lnet_peer_alive_locked() has single caller that only checks whether
zero was returned. We can convert lnet_peer_alive_locked() to return
bool rather than int.

Rename lnet_peer_alive_locked() to lnet_check_message_drop() to
better reflect the purpose of the function. The return value is
inverted to reflect the name change.

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: Iaabdf5109676ffd18bdba9627afea7e041ddc1e1
Reviewed-on: https://review.whamcloud.com/46623
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>