Re-add netd support for enabling IPv6 optimistic mode.

Enables optimistic_dad and use_optimistic on all interfaces
by default.

---

This functionality was originally submitted in ag/569594.  Owing
to issues with bind()ing to optimistic addresses (see b/18609055)
this was reverted in ag/598690.

This reverts the revert.  :-)

Bug: 17769720
Change-Id: I156e5636341a846f41fb9a15c84cf06878b239d8
diff --git a/server/InterfaceController.h b/server/InterfaceController.h
index 71e4344..60e2131 100644
--- a/server/InterfaceController.h
+++ b/server/InterfaceController.h
@@ -32,6 +32,7 @@
 	void setOnAllInterfaces(const char* filename, const char* value);
 	void setAcceptRA(const char* value);
 	void setAcceptRARouteTable(int tableOrOffset);
+	void setIPv6OptimisticMode(const char *value);
 };
 
 #endif