make clat checksum tests more reliable

This is to allow increasing pseudochecksum returned by 0xFFFF,
which is another form of 16-bit 1's complement 0 and thus irrelevant.

Test: builds, atest
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I8cfa04ed1c0bdde2a605cff258a12690748f3bd5
1 file changed