An [IPv6AddressLabel] section accepts the following keys. Specify
several [IPv6AddressLabel] sections to configure several address
labels. IPv6 address labels are used for address selection. See
RFC 3484
[14]. Precedence is managed by userspace, and only the
label itself is stored in the kernel.
Label=
The label for the prefix, an unsigned integer in the range
0–4294967294. 0xffffffff is reserved. This setting is
mandatory.
Prefix=
IPv6 prefix is an address with a prefix length, separated by
a slash "/" character. This key is mandatory.