reset IV method

[moteus]

Now we can not effective implement CTR algorithm with custom counter.
But if we implement resetiv method then we can write:

local aes = crypto.encrypt.new('aes-256-ctr', KEY)
local IV = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}
for b, e in ichunks(msg, block_size) do
  inc_iv(IV)
  aes:resetiv(IV)
  local chunk = string.sub(msg, b, e)
  chunk = aes:update(chunk) -- or even better aes:update(msg, b, e) 
end

I realy do not know is this valid in OpenSSL update iv, but it work.
in my test this method 10 times slower then simple aes-256-crt.
this my implementation moteus-iv