firewall: config: remove restictions on DHCPv6 allow rule

firewall: config: remove restictions on DHCPv6 allow rule

Remove restrictions on source and destination addresses, which aren't
specified on RFC8415, and for some reason in openwrt are configured
to allow both link-local and ULA addresses.
As cleared out in issue #5066 there are some ISPs that use Gloabal
Unicast addresses, so fix this rule to allow them.

Fixes: #5066
Signed-off-by: Tiago Gaspar <tiagogaspar8@gmail.com>
[rebase onto firewall3, clarify subject, bump PKG_RELEASE]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(backported from commit 65258f5d6093809c541050256646795bc0a460a9)