Hi, all
I encountered a problem when trying to configure a static IPv6 route the
nexthop of which is a link-local address.
```
protocol static {
route 2001:db8:1::/48 via fe80::1234%foo;
}
```
The above configuration worked well for routing traffic to 2001:db8:1::/48 to
the router fe80::1234 at the interface named foo. However, if the name of the
interface contains special characters, for example, `foo-bar`, bird will
complain about the syntax.
I dig into the source code and found out that in
https://gitlab.nic.cz/labs/bird/-/blob/legacy/conf/confbase.Y#L162-165,
`ipa_scope` is defined like `%[SYM]`, so in above scenario, the address shall
be expressed as `fe80::1234%'foo-bar'`.
I believe it could be better to have a record of this in user's doc.
Cheers,
Miao Wang
