Ignore country values that are not two characters long

While CentralNotice had a corresponding fix deployed some days ago,
some clients (but 90% fewer in numbers) are still sending session ids.

To get rid of them at once, we now guard against them also on the
server side for some time.

Bug: 66478
Change-Id: I205e4ef5d378db72ceb9bc0390c954fdc9065b05