Use MAX_MSATS instead of magic value

Author: benthecarman

src/amount.rs

@@ -89,8 +89,8 @@ impl Amount {
 	#[inline]
 	pub const fn saturating_add(self, rhs: Amount) -> Amount {
 		match self.0.checked_add(rhs.0) {
-			Some(amt) if amt <= 21_000_000_0000_0000_000 => Amount(amt),
-			_ => Amount(21_000_000_0000_0000_000),
+			Some(amt) if amt <= MAX_MSATS => Amount(amt),
+			_ => Amount(MAX_MSATS),
 		}
 	}