build+face: Fixing regression that broke ethernet support

As of this commit, libpcap is required unless specifically disabled
using --without-libpcap parameter during configure stage.

Change-Id: Iec6f8bd9babfe4da193c98a49043b08319311106
Refs: #1472
diff --git a/daemon/face/ethernet-face.hpp b/daemon/face/ethernet-face.hpp
index 2b4771e..4eaf0b4 100644
--- a/daemon/face/ethernet-face.hpp
+++ b/daemon/face/ethernet-face.hpp
@@ -28,8 +28,8 @@
 #include "ethernet.hpp"
 #include "face.hpp"
 
-#ifndef HAVE_PCAP
-#error "Cannot include this file when pcap is not available"
+#ifndef HAVE_LIBPCAP
+#error "Cannot include this file when libpcap is not available"
 #endif
 
 // forward declarations