rules_generator: net rules - do not print error if file is missing and ignore commented rules

Fix an error message displayed by write_net_rules when the rules file
does not exist yet. (See Debian bugs #442796 and #475699.)

Ignore commented rules, at least for the easy case.
For clarity, use extended instead of standard regular expressions.

extras/rule_generator/rule_generator.functions

@@ -92,6 +92,10 @@ find_all_rules() {
 	local linkre="$2"
 	local match="$3"
 
-	local search='.*[[:space:],]'"$key"'"\('"$linkre"'\)"[[:space:]]*\(,.*\|\\\|\)$'
-	echo $(sed -n -e "${match}s/${search}/\1/p" $RO_RULES_FILE $RULES_FILE 2>/dev/null)
+	local search='[[:space:],]'"$key"'"('"$linkre"')"[[:space:]]*(,.*|\\|)$'
+
+	echo $(sed -n -r -e 's/^#.*//' -e "${match}s/${search}/\1/p" \
+		$RO_RULES_FILE \
+		$([ -e $RULES_FILE ] && echo $RULES_FILE) \
+		2>/dev/null)
 }