enum: Return boolean result for enum_from_name() lookup

Handling the result for enum_from_name() is difficult, as checking for
negative return values requires a cast if the enum type is unsigned. The new
signature clearly differentiates lookup result from lookup value.

Further, this actually allows to convert real -1 enum values, which could not
be distinguished from "not-found" and the -1 return value.

This also fixes several clang warnings where enums are unsigned.

src/conftest/hooks/add_notify.c

@@ -73,8 +73,7 @@ METHOD(listener_t, message, bool,
 		type = atoi(this->type);
 		if (!type)
 		{
-			type = enum_from_name(notify_type_names, this->type);
-			if (type == -1)
+			if (!enum_from_name(notify_type_names, this->type, &type))
 			{
 				DBG1(DBG_CFG, "unknown notify: '%s', skipped", this->type);
 				return TRUE;

src/conftest/hooks/add_payload.c

@@ -77,8 +77,7 @@ METHOD(listener_t, message, bool,
 		type = atoi(this->type);
 		if (!type)
 		{
-			type = enum_from_name(payload_type_short_names, this->type);
-			if (type == -1)
+			if (!enum_from_name(payload_type_short_names, this->type, &type))
 			{
 				DBG1(DBG_CFG, "unknown payload: '%s', skipped", this->type);
 				return TRUE;

src/conftest/hooks/custom_proposal.c

@@ -79,8 +79,7 @@ static linked_list_t* load_proposals(private_custom_proposal_t *this,
 			type = strtoul(key, &end, 10);
 			if (end == key || errno)
 			{
-				type = enum_from_name(transform_type_names, key);
-				if (type == -1)
+				if (!enum_from_name(transform_type_names, key, &type))
 				{
 					DBG1(DBG_CFG, "unknown transform: '%s', skipped", key);
 					continue;

src/conftest/hooks/set_critical.c

@@ -65,8 +65,7 @@ METHOD(listener_t, message, bool,
 			type = atoi(name);
 			if (!type)
 			{
-				type = enum_from_name(payload_type_short_names, name);
-				if (type == -1)
+				if (!enum_from_name(payload_type_short_names, name, &type))
 				{
 					DBG1(DBG_CFG, "invalid payload name '%s'", name);
 					break;

src/conftest/hooks/set_length.c

@@ -63,8 +63,7 @@ METHOD(listener_t, message, bool,
 		type = atoi(this->type);
 		if (!type)
 		{
-			type = enum_from_name(payload_type_short_names, this->type);
-			if (type == -1)
+			if (!enum_from_name(payload_type_short_names, this->type, &type))
 			{
 				DBG1(DBG_CFG, "unknown payload: '%s', skipped", this->type);
 				return TRUE;

src/conftest/hooks/set_reserved.c

@@ -181,8 +181,7 @@ METHOD(listener_t, message, bool,
 			type = atoi(name);
 			if (!type)
 			{
-				type = enum_from_name(payload_type_short_names, name);
-				if (type == -1)
+				if (!enum_from_name(payload_type_short_names, name, &type))
 				{
 					DBG1(DBG_CFG, "invalid payload name '%s'", name);
 					break;

src/conftest/hooks/unencrypted_notify.c

@@ -68,8 +68,7 @@ METHOD(listener_t, ike_updown, bool,
 		type = atoi(this->type);
 		if (!type)
 		{
-			type = enum_from_name(notify_type_names, this->type);
-			if (type == -1)
+			if (!enum_from_name(notify_type_names, this->type, &type))
 			{
 				DBG1(DBG_CFG, "unknown notify: '%s', skipped", this->type);
 				return TRUE;

src/conftest/hooks/unsort_message.c

@@ -69,8 +69,7 @@ METHOD(listener_t, message, bool,
 		order = enumerator_create_token(this->order, ", ", " ");
 		while (order->enumerate(order, &name))
 		{
-			type = enum_from_name(payload_type_short_names, name);
-			if (type != -1)
+			if (enum_from_name(payload_type_short_names, name, &type))
 			{
 				enumerator = list->create_enumerator(list);
 				while (enumerator->enumerate(enumerator, &payload))