Comply with conventions

src/core/iomgr/tcp_server_posix.c

@@ -486,8 +486,8 @@ grpc_tcp_listener *grpc_tcp_server_add_port(grpc_tcp_server *s,
     addr_len = sizeof(addr4_copy);
   }
   sp = add_socket_to_server(s, fd, addr, addr_len);
-  if (sp) sp->sibling = sp2;
-  if (sp2) sp2->is_sibling = 1;
+  if (sp != NULL) sp->sibling = sp2;
+  if (sp2 != NULL) sp2->is_sibling = 1;
 
 done:
   gpr_free(allocated_addr);