usb-storage: Fix share-rw option parsing

usb-storage: Fix share-rw option parsing

Because usb-storage creates an internal scsi device, we should propagate
options. We already do so for bootindex etc, but failed to take care of
share-rw. Fix it in an apparent way: add a new parameter to
scsi_bus_legacy_add_drive and pass in s->conf.share_rw.

Cc: qemu-stable@nongnu.org
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-id: 20180117005222.4781-1-famz@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>