tls: rx: drop unnecessary arguments from tls_setup_from_iter()

sk is unused, remove it to make it clear the function
doesn't poke at the socket.

size_used is always 0 on input and @length on success.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>