Implement Songbird driver configuration (#1074)

src/driver/decode_mode.rs

@@ -0,0 +1,32 @@
+/// Decode behaviour for received RTP packets within the driver.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[non_exhaustive]
+pub enum DecodeMode {
+    /// Packets received from Discord are handed over to events without any
+    /// changes applied.
+    ///
+    /// No CPU work involved.
+    ///
+    /// *BEWARE: this will almost certainly break [user speaking events].
+    /// Silent frame detection only works if extensions can be parsed or
+    /// are not present, as they are encrypted.
+    /// This event requires such functionality.*
+    ///
+    /// [user speaking events]: ../events/enum.CoreEvent.html#variant.SpeakingUpdate
+    Pass,
+    /// Decrypts the body of each received packet.
+    ///
+    /// Small per-packet CPU use.
+    Decrypt,
+    /// Decrypts and decodes each received packet, correctly accounting for losses.
+    ///
+    /// Larger per-packet CPU use.
+    Decode,
+}
+
+impl DecodeMode {
+    /// Returns whether this mode will decrypt received packets.
+    pub fn should_decrypt(self) -> bool {
+        self != DecodeMode::Pass
+    }
+}