The block number is a 16-bit counter which only allows to fetch
files no bigger than 65535 * blksize. To avoid this limit, the
counter is rolled over. This behavior isn't defined in RFC 1350
but is handled by many TFTP servers and it's what GRUB was doing
before implicitly due an overflow.
Closes-Bug: #1938559
Signed-off-by: Jiping Ma <jiping.ma2@windriver.com>
Change-Id: I4a0c04cf15b87f6f40c7a979d20fb3c57657cefd
572cd24c49