l2cap_chan_rx_avail
void l2cap_chan_rx_avail(struct l2cap_chan *chan, ssize_t rx_avail);
l2cap_chan_rx_avail(chan, 0);
l2cap_chan_rx_avail(chan, -1);
l2cap_chan_rx_avail(chan, avail - skb_overhead);
l2cap_chan_rx_avail(chan, -1);