Attach/detach to the listening child socket when accepting TLS

When TLS connection (TLSstream) connection was accepted, the children
listening socket was not attached to sock->server and thus it could have
been freed before all the accepted connections were actually closed.

In turn, this would cause us to call isc_tls_free() too soon - causing
cascade errors in pending SSL_read_ex() in the accepted connections.

Properly attach and detach the children listening socket when accepting
and closing the server connections.

(cherry picked from commit 684f3eb8e6)

lib/isc/netmgr/tlsstream.c

@@ -711,6 +711,7 @@ tlslisten_acceptcb(isc_nmhandle_t *handle, isc_result_t result, void *cbarg) {
 	tlssock = isc_mem_get(handle->sock->mgr->mctx, sizeof(*tlssock));
 	isc__nmsocket_init(tlssock, handle->sock->mgr, isc_nm_tlssocket,
 			   &handle->sock->iface);
+	isc__nmsocket_attach(tlslistensock, &tlssock->server);
 
 	tid = isc_nm_tid();
 	/* We need to initialize SSL now to reference SSL_CTX properly */
@@ -945,6 +946,10 @@ tls_close_direct(isc_nmsocket_t *sock) {
 		isc__nmsocket_detach(&sock->listener);
 	}
 
+	if (sock->server != NULL) {
+		isc__nmsocket_detach(&sock->server);
+	}
+
 	/* Further cleanup performed in isc__nm_tls_cleanup_data() */
 	atomic_store(&sock->closed, true);
 	atomic_store(&sock->active, false);