Linux 4.15: check for 2nd argument to pagevec_init

Linux 4.15: check for 2nd argument to pagevec_init

Linux 4.15 removes the distinction between "hot" and "cold" cache
pages, and pagevec_init() no longer takes a "cold" flag as the
second argument. Add a configure test and use it in osi_vnodeops.c .

Change-Id: Ia5287b409b2a811d2250c274579e6f15fd18fdbb
Reviewed-on: https://gerrit.openafs.org/12824
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Tested-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>