Clean up BtaGattQueue when connected

When BtaGattQueue has a pending task and
if it's disconnected while waiting for
L2CAP connection, GAP_EVT_CONN_CLOSED
is not delivered and BtaGattQueue get stuck.

This change cleans up the queue when connected
to prevent it.

Bug: 343503861
Bug: 379007400
Test: atest bluetooth_csis_test bluetooth_le_audio_client_test bluetooth_has_test
Change-Id: I3c91f5fe9dc052c3fd86689dfcf4ca2106609798