LU-6142 lnet: use list_first_entry() in lnet/lnet subdirectory.

LU-6142 lnet: use list_first_entry() in lnet/lnet subdirectory.

Convert
  list_entry(foo->next .....)
to
  list_first_entry(foo, ....)

in 'lnet/lnet'

In several cases the call is combined with
a list_empty() test and list_first_entry_or_null() is used

Test-Parameters: trivial testlist=sanity-lnet
Change-Id: I45e1bdfe41854c88af98ebf24797f72a68b11dc3
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Reviewed-on: https://review.whamcloud.com/47488
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>