[fixed] ZFS l2arc broken in 10.3

[Peter]

sendbug seems not to work anymore, I end up on websites with marketing- 
babble and finally get asked to provide some login and passwd. :(
But the former mail looks like having come back to me, so it seems I'm 
still allowed to post here...

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*** sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c.orig	Wed Oct 12 21:07:25 2016
--- sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	Wed Oct 12 21:46:16 2016
***************
*** 6508,6514 ****
  			 */
  			buf_sz = hdr->b_size;
  			align = (size_t)1 << dev->l2ad_vdev->vdev_ashift;
! 			buf_a_sz = P2ROUNDUP(buf_sz, align);
  
  			if ((write_asize + buf_a_sz) > target_sz) {
  				full = B_TRUE;
--- 6508,6514 ----
  			 */
  			buf_sz = hdr->b_size;
  			align = (size_t)1 << dev->l2ad_vdev->vdev_ashift;
! 			buf_a_sz = P2ROUNDUP_TYPED(buf_sz, align, uint64_t);
  
  			if ((write_asize + buf_a_sz) > target_sz) {
  				full = B_TRUE;