Clarify TcpSocket::recv_queue() semantics. NFC.

src/socket/tcp.rs

@@ -774,7 +774,9 @@ impl<'a> TcpSocket<'a> {
         self.tx_buffer.len()
     }
 
-    /// Return the amount of octets queued in the receive buffer.
+    /// Return the amount of octets queued in the receive buffer. This value can be larger than
+    /// the slice read by the next `recv` or `peek` call because it includes all queued octets,
+    /// and not only the octets that may be returned as a contiguous slice.
     ///
     /// Note that the Berkeley sockets interface does not have an equivalent of this API.
     pub fn recv_queue(&self) -> usize {