Fix constexpr struct in netlink_request_test.

Credit to haining@ for finding the proper syntax that is supported by
the older compiler.

Bug: 111941923
Test: Built cf_local_image for oc-gce-dev.
Change-Id: I20d91c8e1ac70492acff6f192afddeb869cf35d9
diff --git a/common/libs/net/netlink_request_test.cpp b/common/libs/net/netlink_request_test.cpp
index d819622..03a7dad 100644
--- a/common/libs/net/netlink_request_test.cpp
+++ b/common/libs/net/netlink_request_test.cpp
@@ -186,7 +186,7 @@
     uint16_t attr_type_u8 = kDummyTag + 7;
     uint8_t attr_value_u8 = kValue;
     uint8_t attr_padding_u8[3] = {0, 0, 0};
-  } expected;
+  } expected = {};
 
   cvd::NetlinkRequest request(RTM_SETLINK, 0);
   request.AddInt<int64_t>(kDummyTag, kValue);