test: Mock out MAC address access

This makes it possible for our ethernet interfaces to have MAC Addresses
detected and configured for testing without the system providing a real
NIC.

Change-Id: Ie985efec0a5e393b0b76f3d02bd3015fef6349e4
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/mock_syscall.hpp b/test/mock_syscall.hpp
index f14bd96..4d934b3 100644
--- a/test/mock_syscall.hpp
+++ b/test/mock_syscall.hpp
@@ -1,4 +1,6 @@
 #pragma once
+#include <net/ethernet.h>
+
 #include <string>
 
 /** @brief Adds the given interface and addr info
@@ -12,9 +14,11 @@
 void mock_addIP(const char* name, const char* addr, const char* mask,
                 unsigned int flags);
 
-/** @brief Adds an address string to index mapping
+/** @brief Adds an address string to index mapping and MAC mapping
  *
  *  @param[in] name - Interface name
  *  @param[in] idx  - Interface index
+ *  @param[in] mac  - Interface MAC address
  */
-void mock_addIF(const std::string& name, int idx);
+void mock_addIF(const std::string& name, int idx,
+                const ether_addr& mac = ether_addr{});