Use constant in QueryChannelRange::end_blocknum

Clarifies u32 max value used as the default.

Author: bmancini55

lightning/src/ln/msgs.rs

@@ -1690,7 +1690,7 @@ impl QueryChannelRange {
 	pub fn end_blocknum(&self) -> u32 {
 		match self.first_blocknum.checked_add(self.number_of_blocks) {
 			Some(block) => block,
-			None => 0xffffffff,
+			None => u32::max_value(),
 		}
 	}
 }