linux/uio: remove "skip" offset for UIO_ITER

For UIO_ITER, we are just wrapping a kernel iterator. It will take care
of its own offsets if necessary. We don't need to do anything, and if we
do try to do anything with it (like advancing the iterator by the skip
in zfs_uio_advance) we're just confusing the kernel iterator, ending up
at the wrong position or worse, off the end of the memory region.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17298
(cherry picked from commit 2ee5b51a57)

include/os/linux/spl/sys/uio.h

@@ -151,7 +151,7 @@ zfs_uio_bvec_init(zfs_uio_t *uio, struct bio *bio, struct request *rq)
 #if defined(HAVE_VFS_IOV_ITER)
 static inline void
 zfs_uio_iov_iter_init(zfs_uio_t *uio, struct iov_iter *iter, offset_t offset,
-    ssize_t resid, size_t skip)
+    ssize_t resid)
 {
 	uio->uio_iter = iter;
 	uio->uio_iovcnt = iter->nr_segs;
@@ -161,7 +161,7 @@ zfs_uio_iov_iter_init(zfs_uio_t *uio, struct iov_iter *iter, offset_t offset,
 	uio->uio_fmode = 0;
 	uio->uio_extflg = 0;
 	uio->uio_resid = resid;
-	uio->uio_skip = skip;
+	uio->uio_skip = 0;
 }
 #endif