test/ethernet_interface: Improve syscall test coverage

Change-Id: Ia71a030f2e2e19f2cc191992929ef08d0fa917c2
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/mock_syscall.hpp b/test/mock_syscall.hpp
index 74a693e..8d51e0f 100644
--- a/test/mock_syscall.hpp
+++ b/test/mock_syscall.hpp
@@ -1,6 +1,7 @@
 #pragma once
 #include <net/ethernet.h>
 
+#include <optional>
 #include <string>
 
 /** @brief Clears out the interfaces and IPs configured for mocking
@@ -15,8 +16,7 @@
  *  @param[in] flags - Interface flags.
  */
 
-void mock_addIP(const char* name, const char* addr, const char* mask,
-                unsigned int flags);
+void mock_addIP(const char* name, const char* addr, const char* mask);
 
 /** @brief Adds an address string to index mapping and MAC mapping
  *
@@ -24,5 +24,6 @@
  *  @param[in] idx  - Interface index
  *  @param[in] mac  - Interface MAC address
  */
-void mock_addIF(const std::string& name, int idx,
-                const ether_addr& mac = ether_addr{});
+void mock_addIF(const std::string& name, unsigned idx, unsigned flags = 0,
+                std::optional<ether_addr> mac = std::nullopt,
+                std::optional<unsigned> mtu = std::nullopt);