net: bluetooth: compact struct bt_skb_cb by converting boolean fields to bit fields

Convert boolean fields incoming and req_start to bit fields and move
force_active in order save space in bt_skb_cb in an effort to use
a portion of skb->cb[] for storing skb->dropcount.

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>