Bluetooth: host: introduce timeout in limited advertising

In limited advertising advertising should end after certain timeout.
Previously, limited advertising was just general advertising with
BT_LE_AD_LIMITED flag set. Now, if this flag is set the work is
scheduled, that will disable advertising after timeout.

This affects tests GAP/DISC/LIMM/BV-03-C and GAP/DISC/LIMM/BV-04-C

Signed-off-by: Krzysztof Kopyściński <krzysztof.kopyscinski@codecoup.pl>