face: Fix ioctl() calls on platforms where libpcap uses /dev/bpf*

Change-Id: I2ed2cacf4915458d9b95f0a07beda46039aaa39d
Refs: #2327, #2328
diff --git a/daemon/face/ethernet-face.hpp b/daemon/face/ethernet-face.hpp
index 87e2238..ce72a62 100644
--- a/daemon/face/ethernet-face.hpp
+++ b/daemon/face/ethernet-face.hpp
@@ -100,8 +100,10 @@
 
   /**
    * @brief Enables receiving frames addressed to our MAC multicast group
+   *
+   * @return true if successful, false otherwise
    */
-  void
+  bool
   joinMulticastGroup();
 
   /**