SUNRPC: Convert the backchannel exports to EXPORT_SYMBOL_GPL

Ensure that the backchannel exports conform to the existing sunrpc
practice.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 3c6fe22..6a69a11 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1300,7 +1300,7 @@
 		return 0;
 	}
 }
-EXPORT_SYMBOL(bc_svc_process);
+EXPORT_SYMBOL_GPL(bc_svc_process);
 #endif /* CONFIG_SUNRPC_BACKCHANNEL */
 
 /*