DO NOT MERGE BLE stack doesn't handle multiple l2cap_conn_update requests

we can define 4 bits as flags:
1. L2C_BLE_CONN_UPDATE_DISABLE:
if set it means disable update connection parameter. otherwise enable
2.L2C_BLE_NEW_CONN_PARAM:
if set, it means we have new connection parameter which is needed to be configured
if possible(after update done or enable).
3.L2C_BLE_UPDATE_PENDING:
if set, it means waiting for connection parameter update finished.
this flag will be cleared in btu_ble_ll_conn_param_upd_evt.
will be set when we call btsnd_hcic_ble_upd_ll_conn_params
4.L2C_BLE_NOT_DEFAULT_PARAM:
if set, it means we don't use the default connection parameter.
so when we disable update,
we need to configure default connection parameter.
with these 4 flags, we can replace all these states:
UPD_ENABLED, UPD_DISABLED, UPD_PENDING and UPD_UPDATED.
so we can cover all the corner cases which aren't handled
by original code.

bug:11450715
Change-Id: I6673d4783a8063bf9e8a213c6669800f86e67945