IPv6 6RD web configuration doesn't allow /24 prefix

[blendmaster]

When setting up centurylink's 6RD tunnel, I couldn't set the '6rd Prefix Length' to 24 in the web interface.

1. type in '24' in the text input
2. click 'save' and wait for the button to become enabled again.
3. refresh the page.
4. the '6rd prefix length' is reset back to 32.

However, I was able to set the prefix manually through the shell, as indicated in this post:

nvram set ipv6_6rd_prefix_length="24"
nvram commit

Then, the setting 'sticks', and 6rd tunneling works as expected.

The linked post indicates that other tomato forks besides easytomato also don't set the prefix correctly, so this must be a pretty old bug.