Reject DATAGRAMs larger than the send buffer

Author: zerox80

quinn-proto/src/connection/datagrams.rs

@@ -36,6 +36,9 @@ impl Datagrams<'_> {
             return Err(SendDatagramError::TooLarge);
         }
         if drop {
+            if data.len() > self.conn.config.datagram_send_buffer_size {
+                return Err(SendDatagramError::TooLarge);
+            }
             self.conn.datagrams.drop_until_send_buffer_has_space(
                 data.len(),
                 self.conn.config.datagram_send_buffer_size,