Ensure that addresses have actually been created in TunInterface.

Currently TunInterface assumes that IP addresses are created
immediately as soon as ifc_add_address returns. However, IPv6
addresses, even if created with IFA_F_NODAD or optimistic DAD,
are not created immediately and are not actually usable when the
netlink ACK returns.

Ensure tests aren't flaky by waiting for RTM_NEWADDR for the
address after creating it.

Test: system/netd/tests/runtests.sh
Change-Id: I5db5e25b24329ecbe953b592997b6c1358722c5c
diff --git a/tests/binder_test.cpp b/tests/binder_test.cpp
index 74e5e02..3c00f12 100644
--- a/tests/binder_test.cpp
+++ b/tests/binder_test.cpp
@@ -1334,7 +1334,7 @@
 
     // ... so add a global address.
     const std::string v6 = "2001:db8:1:2:f076:ae99:124e:aa99";
-    EXPECT_EQ(0, ifc_add_address(sTun.name().c_str(), v6.c_str(), 64));
+    EXPECT_EQ(0, sTun.addAddress(v6.c_str(), 64));
 
     // Now expect clatd to start successfully.
     status = mNetd->clatdStart(sTun.name(), nat64Prefix, &clatAddress);