Implement creating VLAN interfaces

Also, minor improvements for TCU:
- added existsAndIsUp convenience function
- added useCanSockets configuration flag

Bug: 156783614
Test: manual
Change-Id: Ia3d48655067792b712519e25ed48ae0cb657347b
diff --git a/automotive/can/1.0/default/libnetdevice/Android.bp b/automotive/can/1.0/default/libnetdevice/Android.bp
index 31e5ad0..6e2c782 100644
--- a/automotive/can/1.0/default/libnetdevice/Android.bp
+++ b/automotive/can/1.0/default/libnetdevice/Android.bp
@@ -25,6 +25,7 @@
         "can.cpp",
         "common.cpp",
         "libnetdevice.cpp",
+        "vlan.cpp",
     ],
     export_include_dirs: ["include"],
 }