wcn36xx: Add ipv6 address tracking

Taking code from iwlwifi this commit adds a standard callback for
ipv6_addr_change().

This callback allows wcn36xx to know the set of ipv6 addresses. Something
we need to know in order to get wowlan working with ipv6.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Tested-by: Benjamin Li <benl@squareup.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210605011140.2004643-6-bryan.odonoghue@linaro.org