vhost: fix mergeable bufs on BE hosts

We copy head count to a 16 bit field, this works by chance on LE but on
BE guest gets 0. Fix it up.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Tested-by: NAlexander Graf <agraf@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/vhost/net.c

@@ -379,7 +379,8 @@ static void handle_rx(struct vhost_net *net)
 		.hdr.gso_type = VIRTIO_NET_HDR_GSO_NONE
 	};
 	size_t total_len = 0;
-	int err, headcount, mergeable;
+	int err, mergeable;
+	s16 headcount;
 	size_t vhost_hlen, sock_hlen;
 	size_t vhost_len, sock_len;
 	/* TODO: check that we are running from vhost_worker? */