[5036] Added \r as a valid whitespace (cf JSON standard)

src/bin/dhcp6/dhcp6_lexer.ll

@@ -66,7 +66,7 @@ unsigned int comment_start_line = 0;
    can be used during actual token definitions. Note some can match
    incorrect inputs (e.g., IP addresses) which must be checked. */
 int   \-?[0-9]+
-blank [ \t]
+blank [ \t\r]
 
 UnicodeEscapeSequence           u[0-9A-Fa-f]{4}
 JSONEscapeCharacter             ["\\/bfnrt]

src/bin/dhcp6/tests/parser_unittest.cc

@@ -274,6 +274,10 @@ TEST(ParserTest, errors) {
               "<string>:1.2: syntax error, unexpected end of file");
     testError("\n", Parser6Context::PARSER_JSON,
               "<string>:2.1: syntax error, unexpected end of file");
+    testError("\t", Parser6Context::PARSER_JSON,
+              "<string>:1.2: syntax error, unexpected end of file");
+    testError("\r", Parser6Context::PARSER_JSON,
+              "<string>:1.2: syntax error, unexpected end of file");
 
     // comments
     testError("# nothing\n",