Fix broken udp_server_test, by adding exec_ctx to read_cb

src/core/iomgr/udp_server.c

@@ -278,7 +278,7 @@ static void on_read(grpc_exec_ctx *exec_ctx, void *arg, int success) {
 
   /* Tell the registered callback that data is available to read. */
   GPR_ASSERT(sp->read_cb);
-  sp->read_cb(sp->emfd, sp->server->grpc_server);
+  sp->read_cb(exec_ctx, sp->emfd, sp->server->grpc_server);
 
   /* Re-arm the notification event so we get another chance to read. */
   grpc_fd_notify_on_read(exec_ctx, sp->emfd, &sp->read_closure);

src/core/iomgr/udp_server.h

@@ -43,7 +43,8 @@ typedef struct grpc_server grpc_server;
 typedef struct grpc_udp_server grpc_udp_server;
 
 /* Called when data is available to read from the socket. */
-typedef void (*grpc_udp_server_read_cb)(grpc_fd *emfd, grpc_server *server);
+typedef void (*grpc_udp_server_read_cb)(grpc_exec_ctx *exec_ctx, grpc_fd *emfd,
+                                        grpc_server *server);
 
 /* Create a server, initially not bound to any ports */
 grpc_udp_server *grpc_udp_server_create(void);

test/core/iomgr/udp_server_test.c

@@ -49,7 +49,8 @@ static grpc_pollset g_pollset;
 static int g_number_of_reads = 0;
 static int g_number_of_bytes_read = 0;
 
-static void on_read(grpc_fd *emfd, grpc_server *server) {
+static void on_read(grpc_exec_ctx *exec_ctx, grpc_fd *emfd,
+                    grpc_server *server) {
   char read_buffer[512];
   ssize_t byte_count;