chunkStrings/chunkInts sized their result with (len+size-1)/size, so a
size near MaxInt wrapped negative and make panicked with "cap out of
range"; count the chunks with div+remainder instead. NormalizeUDPHop's
len-hops+1 is bounded by len(masks) since hops >= 1, so cap at that.
Resolves CodeQL go/allocation-size-overflow alerts #119 and #120.