L2CAP: Handle no idle timeout (0xFFFF)

Precondition:
1. DUT acts as GATT server.
2. Remote acts as Gatt Client

Use case:
1. Remote device starts BLE scan
2. Remote device connects to DUT
3. Remote device keeps on sending notifications to DUT

Expected result:
Connection should be active after 18 hours

Observed Result:
Connection is dropped after 18 hours due to l2c_link_timeout.

Root Cause:
L2CAP is not properly handling no idle timeout(0xFFFF) and 65535000 ms
timer gets started after BLE connection, leading to connection getting dropped
after 18 hours.

Fix:
If there is no L2CAP dynamic ccb and no idle timeout is configured for
GATT or any other fixed  channel, then cancel existing LCB timer.

Test: No BLE disconnection seen after 18 hours

Bug: 112249120
Change-Id: I58766564cf62efb7af0869035115459bae37c558