Bluetooth: HCI: Add handle to conn param update command complete

The BT_HCI_OP_LE_CONN_PARAM_REQ_REPLY and
BT_HCI_OP_LE_CONN_PARAM_REQ_NEG_REPLY command complete events contain
a connection handle that serves to match the command with their
corresponding command complete event when there's more than one
pending. For now this just adds the structure definitions required,
and later on code will need to be added to handle possible mismatches.

Change-Id: I4585888b32ec995b18847c2a6ed488a2da9c8520
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>