NETMAP and off-by-one?

[Slawa Olhovchenkov]

I am see strange things: like NETMAP stop transmit after `head` and `cur`
touch `tail`.

But:

/*
 * check if space is available in the ring.
 */
static inline int
nm_ring_empty(struct netmap_ring *ring)
{
        return (ring->cur == ring->tail);
}

i.e. if cur == (tail-1) mod ring_size -- space is available in the
ring and I can put packet in output buffer.
After put this packet ring is full, but no transmiting.

This is bug?