Bluetooth: Update conf_state before send config_req out

Update conf_state with L2CAP_CONF_REQ_SENT before send config_req out in
l2cap_config_req().

Signed-off-by: Haijun Liu <haijun.liu@atheros.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>