Bluetooth: SMP: Fix using nano_delayed_work API

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

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

Change-Id: Ida58ff0f609dc2a8fd415692bc2cec91eb56a294
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>