rxrpc: Support service upgrade from a kernel service

Provide support for a kernel service to make use of the service upgrade
facility.  This involves:

 (1) Pass an upgrade request flag to rxrpc_kernel_begin_call().

 (2) Make rxrpc_kernel_recv_data() return the call's current service ID so
     that the caller can detect service upgrade and see what the service
     was upgraded to.

Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 82e1655..3f03f78 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -100,6 +100,7 @@ struct afs_call {
 	bool			send_pages;	/* T if data from mapping should be sent */
 	bool			need_attention;	/* T if RxRPC poked us */
 	bool			async;		/* T if asynchronous */
+	bool			upgrade;	/* T to request service upgrade */
 	u16			service_id;	/* RxRPC service ID to call */
 	__be16			port;		/* target UDP port */
 	u32			operation_ID;	/* operation ID for an incoming call */