lib/tun.c: generalize tun_*route() to netdev_*route()

There's nothing specific to tun devices in adding a route to the kernel.

Change-Id: Ib077934aa5f3c9bed06e2cf16a980c965a7a046d
diff --git a/sgsnemu/sgsnemu.c b/sgsnemu/sgsnemu.c
index 99f56da..8903d81 100644
--- a/sgsnemu/sgsnemu.c
+++ b/sgsnemu/sgsnemu.c
@@ -1437,7 +1437,7 @@
 		if (options.defaultroute) {
 			struct in_addr rm;
 			rm.s_addr = 0;
-			tun_addroute(tun, &rm, &addr.v4, &rm);
+			netdev_addroute(&rm, &addr.v4, &rm);
 		}
 		if (options.ipup)
 			tun_runscript(tun, options.ipup);
@@ -1588,7 +1588,7 @@
 		if (options.defaultroute) {
 			struct in_addr rm;
 			rm.s_addr = 0;
-			tun_addroute(tun, &rm, &options.destaddr.v4, &rm);
+			netdev_addroute(&rm, &options.destaddr.v4, &rm);
 		}
 		if (options.ipup)
 			tun_runscript(tun, options.ipup);