more dos protection (#8104)

ethcore/vm/src/schedule.rs

@@ -135,6 +135,8 @@ pub struct WasmCosts {
 	pub initial_mem: u32,
 	/// Grow memory cost, per page (64kb)
 	pub grow_mem: u32,
+	/// Memory copy cost, per byte
+	pub memcpy: u32,
 	/// Max stack height (native WebAssembly stack limiter)
 	pub max_stack_height: u32,
 	/// Cost of wasm opcode is calculated as TABLE_ENTRY_COST * `opcodes_mul` / `opcodes_div`
@@ -154,6 +156,7 @@ impl Default for WasmCosts {
 			static_address: 40,
 			initial_mem: 4096,
 			grow_mem: 8192,
+			memcpy: 1,
 			max_stack_height: 64*1024,
 			opcodes_mul: 3,
 			opcodes_div: 8,