dirty-bitmap: Report BlockDirtyInfo.count in bytes, as documented

dirty-bitmap: Report BlockDirtyInfo.count in bytes, as documented

We've been documenting the value in bytes since its introduction
in commit b9a9b3a4 (v1.3), where it was actually reported in bytes.

Commit e4654d2 (v2.0) then removed things from block/qapi.c, in
preparation for a rewrite to a list of dirty sectors in the next
commit 21b5683 in block.c, but the new code mistakenly started
reporting in sectors.

Fixes: https://bugzilla.redhat.com/1441460
CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 6c98c57af3f4fab85bdf5f01616c91322bd4312a)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>