Fixes #9542

This fixes the case when a server is shutdown right after it Accept'ed
a connection. The socket needs to be closed right before the endpoint
is destroyed.
diff --git a/src/core/ext/transport/chttp2/server/chttp2_server.c b/src/core/ext/transport/chttp2/server/chttp2_server.c
index b9c62c3..2c076e8 100644
--- a/src/core/ext/transport/chttp2/server/chttp2_server.c
+++ b/src/core/ext/transport/chttp2/server/chttp2_server.c
@@ -127,6 +127,7 @@
   gpr_mu_lock(&state->mu);
   if (state->shutdown) {
     gpr_mu_unlock(&state->mu);
+    grpc_endpoint_shutdown(exec_ctx, tcp, GRPC_ERROR_NONE);
     grpc_endpoint_destroy(exec_ctx, tcp);
     gpr_free(acceptor);
     return;