tools: switch to Face::getIoContext()

Change-Id: I6be4c682d62e1061af45052d2141b9e5b9e897c5
diff --git a/tools/nfdc/face-helpers.cpp b/tools/nfdc/face-helpers.cpp
index 36982a4..780422f 100644
--- a/tools/nfdc/face-helpers.cpp
+++ b/tools/nfdc/face-helpers.cpp
@@ -186,7 +186,7 @@
   uri.canonize(
     [&result] (const auto& canonicalUri) { result = canonicalUri; },
     [&error] (const auto& errorReason) { error = errorReason; },
-    ctx.face.getIoService(), ctx.getTimeout());
+    ctx.face.getIoContext(), ctx.getTimeout());
   ctx.face.processEvents();
 
   return {result, error};