Bluetooth: Add module parameter for txWindow size on L2CAP

Very useful for testing purposes.
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
[jprvita@profusion.mobi: improved parameter description]
Signed-off-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap.c

@@ -57,6 +57,7 @@
 
 static int enable_ertm = 0;
 static int max_transmit = L2CAP_DEFAULT_MAX_TX;
+static int tx_window = L2CAP_DEFAULT_TX_WINDOW;
 
 static u32 l2cap_feat_mask = L2CAP_FEAT_FIXED_CHAN;
 static u8 l2cap_fixed_chan[8] = { 0x02, };
@@ -791,7 +792,7 @@ static void l2cap_sock_init(struct sock *sk, struct sock *parent)
 		pi->omtu = 0;
 		pi->mode = L2CAP_MODE_BASIC;
 		pi->fcs  = L2CAP_FCS_CRC16;
-		pi->tx_win = L2CAP_DEFAULT_TX_WINDOW;
+		pi->tx_win = tx_window;
 		pi->sec_level = BT_SECURITY_LOW;
 		pi->role_switch = 0;
 		pi->force_reliable = 0;
@@ -4296,6 +4297,9 @@ MODULE_PARM_DESC(enable_ertm, "Enable enhanced retransmission mode");
 module_param(max_transmit, uint, 0644);
 MODULE_PARM_DESC(max_transmit, "Max transmit value (default = 3)");
 
+module_param(tx_window, uint, 0644);
+MODULE_PARM_DESC(tx_window, "Transmission window size value (default = 63)");
+
 MODULE_AUTHOR("Marcel Holtmann <marcel@holtmann.org>");
 MODULE_DESCRIPTION("Bluetooth L2CAP ver " VERSION);
 MODULE_VERSION(VERSION);