resolved: have the stub resolver listen on both TCP and UDP by default

RFC7766 section 4 states that in the absence of EDNS0, a response that
is too large for a 512-byte UDP packet will have the 'truncated' bit
set. The client is expected to retry the query over TCP.

Fixes #10264.

src/resolve/resolved-manager.c

@@ -580,7 +580,7 @@ int manager_new(Manager **ret) {
                 .dnssec_mode = DEFAULT_DNSSEC_MODE,
                 .dns_over_tls_mode = DEFAULT_DNS_OVER_TLS_MODE,
                 .enable_cache = true,
-                .dns_stub_listener_mode = DNS_STUB_LISTENER_UDP,
+                .dns_stub_listener_mode = DNS_STUB_LISTENER_YES,
                 .read_resolv_conf = true,
                 .need_builtin_fallbacks = true,
                 .etc_hosts_last = USEC_INFINITY,

src/resolve/resolved.conf.in

@@ -20,5 +20,5 @@
 #DNSSEC=@DEFAULT_DNSSEC_MODE@
 #DNSOverTLS=@DEFAULT_DNS_OVER_TLS_MODE@
 #Cache=yes
-#DNSStubListener=udp
+#DNSStubListener=yes
 #ReadEtcHosts=yes