Ok, that parses somehow in Python, matches, and is apparently legit. ;-)

    >>> from ipaddress import IPv6Address as address
    >>> address('2001:db8::192.168.0.42')
    IPv6Address('2001:db8::c0a8:2a')
    >>> int('2a', 16)
    42

Openwrt doesn't seem to make ipv6 static assignment easy unfortunately.