brctl: fix compilation error

Fix compilation error due to field 'ip6' which
has incomplete type

CRs-fixed: 665103
Change-Id: Ia427dd12cb3f959afd1dca7ad99311f46f374130
diff --git a/libbridge/libbridge.h b/libbridge/libbridge.h
index e7506e0..2fe4857 100644
--- a/libbridge/libbridge.h
+++ b/libbridge/libbridge.h
@@ -21,6 +21,7 @@
 
 #include <sys/socket.h>
 #include <linux/if.h>
+#include <linux/in6.h>
 #include <linux/if_bridge.h>
 #ifdef FEATURE_ANDROID
 #include <sys/time.h>