Bluetooth: controller: Prevent LLCP handling of must-expire events

When a must-expire ticker callback is executed, it is important not to
call the LLCP state machine, as the lazy state is unavailable. The code
must rely on the next proper event to call ull_conn_llcp with an updated
non-zero lazy count.

Signed-off-by: Morten Priess <mtpr@oticon.com>