Bluetooth: Workaround privacy feature issue

This fixes intercompatibility issues with controllers supporting
privacy feature.
Core Spec requires to use network privacy mode as a default when
peer device provides its IRK during bonding when LL Privacy is used,
which is the case for Zephyr. We've seen devices including PTS
which exchanges it's IRK but is not aware about network privacy
mode. This results in Zephyr not able do be reconnect to such bonded
devices.
This workaround sets device privacy mode to be able to reconnect
to such devices.

Fixes #4989
Fixes #5486

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>