sha1: Fix algorithm for data bigger than 512 megabytes.

sha1: Fix algorithm for data bigger than 512 megabytes.

In modern systems, size_t is 64 bits. There is a 32 bit overflow check
in sha1_update(), which will not work correctly, because compiler will
do an automatic cast to 64 bits, since size_t type variable is in the
expression. We do want however to lose data, since this is the whole
idea of this overflow check.

Because of this, computation of SHA-1 checksum will always be incorrect
for any data, that is bigger than 512 megabytes, which in bits is the
boundary of 32 bits integer.

In practice it means that any OVSDB transaction, bigger or equal to 512
megabytes, is considered corrupt and ovsdb-server will refuse to work
with the database file. This is especially critical for OVN southbound
database, since it tends to grow rapidly.

Fixes: 5eccf359391f ("Replace SHA-1 library with one that is clearly licensed.")
Signed-off-by: Renat Nurgaliyev <impleman@gmail.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>