udp: config: make max_connection_age a u32, improve its documentation

aquatic_udp/src/common.rs

@@ -34,7 +34,7 @@ impl ConnectionValidator {
         Ok(Self {
             hmac,
             start_time: Instant::now(),
-            max_connection_age: config.cleaning.max_connection_age as u32,
+            max_connection_age: config.cleaning.max_connection_age,
         })
     }
 

aquatic_udp/src/config.rs

@@ -171,8 +171,8 @@ pub struct CleaningConfig {
     /// lingering for a long time. However, the cleaning also returns unused
     /// allocated memory to the OS, so the interval can be configured here.
     pub pending_scrape_cleaning_interval: u64,
-    /// Maximum time to use a connection token before it expires (seconds)
-    pub max_connection_age: u64,
+    /// Allow clients to use a connection token for this long (seconds)
+    pub max_connection_age: u32,
     /// Remove peers who have not announced for this long (seconds)
     pub max_peer_age: u64,
     /// Remove pending scrape responses that have not been returned from request