luci-proto-ipv6: dhcpv6.js: make reqaddress modes translatable

Fixes: #6730, #6751
Fixes: 2065ead4

 ("luci-proto-ipv6: dhcpv6.js fix translation (#6751)")
Suggested-by: he ping <pinghejk@gmail.com>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>