Constify failed_before_recv_message check (#26330)

* Constify failed recv_message check

* Update call.h

src/core/lib/surface/call.cc

@@ -2017,7 +2017,7 @@ grpc_compression_algorithm grpc_call_compression_for_level(
   return algo;
 }
 
-bool grpc_call_failed_before_recv_message(grpc_call* c) {
+bool grpc_call_failed_before_recv_message(const grpc_call* c) {
   return c->call_failed_before_recv_message;
 }
 

src/core/lib/surface/call.h

@@ -124,7 +124,7 @@ grpc_compression_algorithm grpc_call_compression_for_level(
  * an error (as opposed to a graceful end-of-stream) */
 /* TODO(markdroth): This is currently available only to the C++ API.
                     Move to surface API if requested by other languages. */
-bool grpc_call_failed_before_recv_message(grpc_call* c);
+bool grpc_call_failed_before_recv_message(const grpc_call* c);
 
 extern grpc_core::TraceFlag grpc_call_error_trace;
 extern grpc_core::TraceFlag grpc_compression_trace;