Bluetooth: Expose debugfs settings for LE connection interval

For testing purposes expose the default LE connection interval values
via debugfs.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

diff --cc include/net/bluetooth/hci_core.h
Simple merge

diff --cc net/bluetooth/hci_conn.c
Simple merge

diff --cc net/bluetooth/hci_core.c
Simple merge