Configure IPv6 for WWAN interface

I get IPv6 on my LTE modem and I create a dynamic DHCPv6 interface with:

ubus call network add_dynamic  { "name": "wwan6", "ifname": "@wwan", "proto": "dhcpv6", "metric": 10, "extendprefix": "1", "dns": [ "1234:4567:0013:0000:0000:0000:0000:0001", "1234:4567:0013:0000:0000:0000:0000:0002" ], "zone": "wan" }

Everything is okay and clients can access IPv6 addresses. But after 18 hours I get No default route present, overriding ra_lifetime!.

I can see from TCPdump that the router is sending Router Solicitation and I get Router Advertisment back. The router is also sending DHCPv6 Solitcit message, but no response.

In Router Advertisement Router lifetime is 64800s (18h).
How do I turn off DHCPv6 solicit message and how do I activate a new Router Solicitation message within 18h?