prototype implementation of connect-ethernet

https://www.ietf.org/id/draft-asedeno-masque-connect-ethernet-00.html

PiperOrigin-RevId: 550375485
diff --git a/quiche/quic/masque/masque_server_backend.cc b/quiche/quic/masque/masque_server_backend.cc
index d7ccb9a..a40ecc0 100644
--- a/quiche/quic/masque/masque_server_backend.cc
+++ b/quiche/quic/masque/masque_server_backend.cc
@@ -37,7 +37,8 @@
   auto protocol_pair = request_headers.find(":protocol");
   if (method != "CONNECT" || protocol_pair == request_headers.end() ||
       (protocol_pair->second != "connect-udp" &&
-       protocol_pair->second != "connect-ip")) {
+       protocol_pair->second != "connect-ip" &&
+       protocol_pair->second != "connect-ethernet")) {
     // This is not a MASQUE request.
     return false;
   }