LU-14291 ptlrpc: support nrs_delay for client-only builds

LU-14291 ptlrpc: support nrs_delay for client-only builds

nrs_delay is intended for use on the client, but is currently disabled
for client-only builds.  So move the ptlrpc_nrs_policy_register() call
outside of the #ifdef.

Also change the nrs modules that *are* server-only to not have #ifdef
in the C file, but that rather to be identified in the Makefile as
only being built when server code is wanted.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Ie25ed5ac837ff5f891824fad31ab258923840ec0
Reviewed-on: https://review.whamcloud.com/41127
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>