Bluetooth: ISO: Update hci_conn_hash_lookup_big for Broadcast slave

Currently, hci_conn_hash_lookup_big only checks for BIS master connections,
by filtering out connections with the destination address set. This commit
updates this function to also consider BIS slave connections, since it is
also used for a Broadcast Receiver to set an available BIG handle before
issuing the LE BIG Create Sync command.

Signed-off-by: Iulia Tanasescu <iulia.tanasescu@nxp.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>