Add stub for kernel_interface_operational.

kernel.h

@@ -37,6 +37,7 @@ struct kernel_route {
 int kernel_setup(int setup, int ipv4);
 int kernel_setup_socket(int setup);
 int kernel_setup_interface(int setup, const char *ifname, int ifindex);
+int kernel_interface_operational(const char *ifname, int ifindex);
 int kernel_interface_ipv4(const char *ifname, int ifindex, char *addr_r);
 int kernel_interface_mtu(const char *ifname, int ifindex);
 int kernel_interface_wireless(const char *ifname, int ifindex);

kernel_netlink.c

@@ -531,6 +531,12 @@ kernel_setup_interface(int setup, const char *ifname, int ifindex)
     return 1;
 }
 
+int
+kernel_interface_operational(const char *ifname, int ifindex)
+{
+    return 1;
+}
+
 int
 kernel_interface_ipv4(const char *ifname, int ifindex, char *addr_r)
 {

kernel_socket.c

@@ -220,6 +220,12 @@ kernel_setup_interface(int setup, const char *ifname, int ifindex)
     return 1;
 }
 
+int
+kernel_interface_operational(const char *ifname, int ifindex)
+{
+    return 1;
+}
+
 int
 kernel_interface_ipv4(const char *ifname, int ifindex, char *addr_r)
 {