Bluetooth: conn: Fix using nano_delayed_work API

This fixes warnings related to the use of nano_work and
nano_delayed_work in bt_conn layer.

Note that k_delayed_work takes a timeout in miliseconds rather than in
ticks thus the timeout values have been changed.

Change-Id: Ia8f34b475051515fd74000cce745ad226aa18aa5
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>