Bluetooth: Add support for rotating RPA

If privacy is enabled we always use RPA, even for active scan.
This makes single point of controlling current random address
making code simple and not prone to subtle bugs with concurent
advertising, scanning and connecting.

Currently used RPA is rotated to improve privacy. Timeout value is
controlled by Kconfig and by default is 900 seconds (15 minutes).

Change-Id: I27a15666a4f2e2962cf6eb20c7cd06f90b7f2bb1
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>