floss: GATT: Make sure OnConnectionUpdated is sent when ConnectionParameterUpdate

When ConnectionParameterUpdate is called without an GATT connnection,
LibBluetooth won't send out a callback. To provide a simpler API usage,
this patch guarantees that a OnConnectionUpdated will always be sent
after ConnectionParameterUpdate.

Bug: 372547952
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: manual call ConnectionParameterUpdate w/o an active connection,
      the OnConnectionUpdated callback is called
Flag: EXEMPT, Floss-only change
Change-Id: Ib22b235ce2a6cb38d93ca9fa1e2d24a60b25223b