netdev-bsd: Fix compiling error in netbsd.

In some netbsd version, RTF_LLINFO is undefined.

Signed-off-by: Hui Kang <hkang.sunysb@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/netdev-bsd.c

@@ -1357,7 +1357,11 @@ netdev_bsd_arp_lookup(const struct netdev *netdev OVS_UNUSED,
     mib[2] = 0;
     mib[3] = AF_INET;
     mib[4] = NET_RT_FLAGS;
+#ifdef RTF_LLINFO
     mib[5] = RTF_LLINFO;
+#else
+    mib[5] = 0;
+#endif
     if (sysctl(mib, 6, NULL, &needed, NULL, 0) == -1) {
         error = errno;
         goto error;