Mark SIG(0) quota settings as experimantal

A different solution in the future might be adopted depending
on feedback and other new information, so it makes sense to mark
these options as EXPERIMENTAL until we have more data.

doc/misc/options

@@ -277,8 +277,8 @@ options {
 	sig-signing-signatures <integer>;
 	sig-signing-type <integer>;
 	sig-validity-interval <integer> [ <integer> ]; // obsolete
-	sig0checks-quota <integer>;
-	sig0checks-quota-exempt { <address_match_element>; ... };
+	sig0checks-quota <integer>; // experimental
+	sig0checks-quota-exempt { <address_match_element>; ... }; // experimental
 	sortlist { <address_match_element>; ... }; // deprecated
 	stale-answer-client-timeout ( disabled | off | <integer> );
 	stale-answer-enable <boolean>;

lib/isccfg/namedconf.c

@@ -1361,8 +1361,9 @@ static cfg_clausedef_t options_clauses[] = {
 	{ "session-keyalg", &cfg_type_astring, 0 },
 	{ "session-keyfile", &cfg_type_qstringornone, 0 },
 	{ "session-keyname", &cfg_type_astring, 0 },
-	{ "sig0checks-quota", &cfg_type_uint32, 0 },
-	{ "sig0checks-quota-exempt", &cfg_type_bracketed_aml, 0 },
+	{ "sig0checks-quota", &cfg_type_uint32, CFG_CLAUSEFLAG_EXPERIMENTAL },
+	{ "sig0checks-quota-exempt", &cfg_type_bracketed_aml,
+	  CFG_CLAUSEFLAG_EXPERIMENTAL },
 	{ "sit-secret", NULL, CFG_CLAUSEFLAG_ANCIENT },
 	{ "stacksize", &cfg_type_size, CFG_CLAUSEFLAG_ANCIENT },
 	{ "startup-notify-rate", &cfg_type_uint32, 0 },