Bluetooth: LE advertising cache

This patch implements the LE advertising cache. It stores sensitive
information (bdaddr and bdaddr_type so far) gathered from LE
advertising report events.

Only advertising entries from connectables devices are added to the
cache.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>