drbd: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()

Use sendmsg() conditionally with MSG_SPLICE_PAGES in _drbd_send_page()
rather than calling sendpage() or _drbd_no_send_page().

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Philipp Reisner <philipp.reisner@linbit.com>
cc: Lars Ellenberg <lars.ellenberg@linbit.com>
cc: "Christoph Böhmwalder" <christoph.boehmwalder@linbit.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: drbd-dev@lists.linbit.com
Link: https://lore.kernel.org/r/20230623225513.2732256-11-dhowells@redhat.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>