re-add grpc_set_socket_ipv6...

src/core/iomgr/socket_utils_common_posix.c

@@ -99,6 +99,16 @@ int grpc_set_socket_ip_pktinfo_if_possible(int fd) {
 #endif
 }
 
+int grpc_set_socket_ipv6_recvpktinfo_if_possible(int fd) {
+#ifdef GPR_HAVE_IPV6_RECVPKTINFO
+  int get_local_ip = 1;
+  return setsockopt(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &get_local_ip,
+                    sizeof(get_local_ip));
+#else
+  return 1;
+#endif
+}
+
 /* set a socket to close on exec */
 int grpc_set_socket_cloexec(int fd, int close_on_exec) {
   int oldflags = fcntl(fd, F_GETFD, 0);