Bluetooth: Make l2cap_ertm_data_rcv static

It is not used outside of l2cap_core.c. Also l2cap_ertm_data_rcv is
only used after it is defined so there is no need for forward declaration.
Signed-off-by: Szymon Janc <szymon.janc@tieto.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

net/bluetooth/l2cap_core.c

@@ -73,8 +73,6 @@ static int l2cap_build_conf_req(struct l2cap_chan *chan, void *data);
 static void l2cap_send_disconn_req(struct l2cap_conn *conn,
 				struct l2cap_chan *chan, int err);
 
-static int l2cap_ertm_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb);
-
 /* ---- L2CAP channels ---- */
 
 static struct l2cap_chan *__l2cap_get_chan_by_dcid(struct l2cap_conn *conn, u16 cid)
@@ -4146,7 +4144,7 @@ static inline int l2cap_data_channel_sframe(struct l2cap_chan *chan, u32 rx_cont
 	return 0;
 }
 
-int l2cap_ertm_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb)
+static int l2cap_ertm_data_rcv(struct l2cap_chan *chan, struct sk_buff *skb)
 {
 	u32 control;
 	u16 req_seq;