RFCOMM_SKB_HEAD_RESERVE
#define RFCOMM_SKB_RESERVE (RFCOMM_SKB_HEAD_RESERVE + RFCOMM_SKB_TAIL_RESERVE)
skb = bt_skb_sendmmsg(sk, msg, len, d->mtu, RFCOMM_SKB_HEAD_RESERVE,
skb_reserve(skb, RFCOMM_SKB_HEAD_RESERVE);