Bluetooth: Add Kconfig option for L2CAP Extended Features

The L2CAP Extended Features are still unstable and under development,
so we are adding them under the EXPERIMENTAL flag to get more feedback
on them. L2CAP Extended Features includes the Enhanced Retransmission
and Streaming Modes, Frame Check Sequence (FCS), and Segmentation and
Reassemby (SAR).

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 187f46d..4c00720 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -55,7 +55,11 @@
 
 #define VERSION "2.14"
 
+#ifdef CONFIG_BT_L2CAP_EXT_FEATURES
+static int enable_ertm = 1;
+#else
 static int enable_ertm = 0;
+#endif
 static int max_transmit = L2CAP_DEFAULT_MAX_TX;
 static int tx_window = L2CAP_DEFAULT_TX_WINDOW;