Bluetooth: Move hci_abort_conn to hci_conn.c

hci_abort_conn() is a wrapper around a number of DISCONNECT and
CREATE_CONN_CANCEL commands that was being invoked from hci_request
request queues, which are now deprecated. There are two versions:
hci_abort_conn() which can be invoked from the hci_event thread, and
hci_abort_conn_sync() which can be invoked within a hci_sync cmd chain.

Signed-off-by: Brian Gix <brian.gix@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>