face: move common declarations to face-common.hpp

Change-Id: I0e3e7a93f0693b0e24ca67493a4229987e792ef4
diff --git a/tests/daemon/face/ethernet-channel.t.cpp b/tests/daemon/face/ethernet-channel.t.cpp
index c1311da..950bdd2 100644
--- a/tests/daemon/face/ethernet-channel.t.cpp
+++ b/tests/daemon/face/ethernet-channel.t.cpp
@@ -24,6 +24,7 @@
  */
 
 #include "face/ethernet-channel.hpp"
+#include "face/face.hpp"
 
 #include "tests/test-common.hpp"
 #include "ethernet-fixture.hpp"