Syzbot hit warning in hci_conn_del() caused by freeing handle that was
not allocated using ida allocator.

This is caused by handle bigger than HCI_CONN_HANDLE_MAX passed by
hci_le_big_sync_established_evt(), which makes code think it's unset
connection.

Add same check for handle upper bound as in hci_conn_set_handle() to
prevent warning.

Link: https://syzkaller.appspot.com/bug?extid=b2545b087a01a7319474
Reported-by: syzbot+b2545b087a01a7319474@syzkaller.appspotmail.com
Fixes: 181a42ed ("Bluetooth: Make handle of hci_conn be unique")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>