Don't fail if getting SO_BINDTODEVICE is not yet supported.

This makes sock_diag_test pass on android-3.4.

Change-Id: Iba2afc09b62e59e03c1368e9d1772da685ab0300
diff --git a/net/test/sock_diag.py b/net/test/sock_diag.py
index 8089947..58faccf 100755
--- a/net/test/sock_diag.py
+++ b/net/test/sock_diag.py
@@ -195,7 +195,10 @@
     """Creates an InetDiagReqV2 that matches the specified socket."""
     family = s.getsockopt(net_test.SOL_SOCKET, net_test.SO_DOMAIN)
     protocol = s.getsockopt(net_test.SOL_SOCKET, net_test.SO_PROTOCOL)
-    iface = s.getsockopt(SOL_SOCKET, net_test.SO_BINDTODEVICE)
+    if net_test.LINUX_VERSION >= (3, 8):
+      iface = s.getsockopt(SOL_SOCKET, net_test.SO_BINDTODEVICE)
+    else:
+      iface = 0
     src, sport = s.getsockname()[:2]
     try:
       dst, dport = s.getpeername()[:2]