LU-13255 lnet: introduce wait_var_event_warning.

LU-13255 lnet: introduce wait_var_event_warning.

LNet has a recurring pattern of waiting for some variable to reach a
particular value, and generating a warning every second that it
hasn't.  In many cases the warning has a higher priority if the wait
has been for a power-of-2 seconds.

This patch embodies that pattern in a new macro
  wait_var_event_warning()

and uses wake_up_var() to cause the wait to complete as soon as
possible.

This patch does not include any change to gnilnd - that is left for
a separate patch.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I557a64713cbe379a566a775944f58ddf93dbd800
Reviewed-on: https://review.whamcloud.com/37593
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>