samples: bluetooth: Increase sync timeout to allow packet loss

The periodic advertiser samples use a periodic advertising interval
in the range of 1 to 1.2 seconds.

Previously the sync timeout of 1.7 seconds would cause the sync to be
lost after failing to receive a single periodic advertising packet.
This change therefore aims to improve the user experience.

Signed-off-by: Rubin Gerritsen <rubin.gerritsen@nordicsemi.no>