resolv: Unify sockaddr union

Merge the following unions into a single union.
sockaddr_union
_sockaddr_union
res_sockaddr_union

Test: netd_{unit,integration}_test pass
Change-Id: I46685e7380dd25070ccd9eaf5387efde91cded8a
diff --git a/resolv/include/netd_resolv/resolv.h b/resolv/include/netd_resolv/resolv.h
index e921958..6bf1bdd 100644
--- a/resolv/include/netd_resolv/resolv.h
+++ b/resolv/include/netd_resolv/resolv.h
@@ -36,6 +36,12 @@
 
 #include "params.h"
 
+typedef union sockaddr_union {
+    struct sockaddr sa;
+    struct sockaddr_in sin;
+    struct sockaddr_in6 sin6;
+} sockaddr_union;
+
 /*
  * Passing NETID_UNSET as the netId causes system/netd/server/DnsProxyListener.cpp to
  * fill in the appropriate default netId for the query.