Bluetooth: Initial support for retransmission of packets with REJ frames

When receiving an I-frame with unexpected txSeq, receiver side start the
recovery procedure by sending a REJ S-frame to the transmitter side. So
the transmitter can re-send the lost I-frame.

This patch just adds a basic support for retransmission, it doesn't
mean that ERTM now has full support for packet retransmission.

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
index 0afde8d..a1d8ec4 100644
--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -351,6 +351,7 @@
 #define L2CAP_CONF_MAX_CONF_RSP 2
 
 #define L2CAP_CONN_SAR_SDU         0x01
+#define L2CAP_CONN_UNDER_REJ       0x02
 
 static inline int l2cap_tx_window_full(struct sock *sk)
 {