[fix] net/dhcpcd pkg-readme update

I propose changing "from fe80::/10" (and the recently added to ff02::1:2) to "from any", "to any".

There was recently an issue where an ISP was sending DHCPv6 PD advertisements from a global address, and the dhcpcd maintainer weighed in here:
https://github.com/NetworkConfiguration/dhcpcd/issues/170#issuecomment-1387318448



$ cvs diff -u ports/net/dhcpcd/pkg/README
Index: ports/net/dhcpcd/pkg/README
===================================================================
RCS file: /cvs/ports/net/dhcpcd/pkg/README,v
retrieving revision 1.13
diff -u -r1.13 README
--- ports/net/dhcpcd/pkg/README 8 Jan 2023 10:01:02 -0000 1.13
+++ ports/net/dhcpcd/pkg/README 18 Jan 2023 16:29:23 -0000
@@ -14,8 +14,8 @@

Also ensure that pf.conf(5) allows DHCPv6 traffic to pass, for example:

- pass in quick on pppoe0 proto udp from fe80::/10 port dhcpv6-server to fe80::/10 port dhcpv6-client
- pass out quick on pppoe0 proto udp from fe80::/10 port dhcpv6-client to ff02::1:2 port dhcpv6-server
+ pass in quick on pppoe0 proto udp from any port dhcpv6-server to fe80::/10 port dhcpv6-client
+ pass out quick on pppoe0 proto udp from fe80::/10 port dhcpv6-client to any port dhcpv6-server

As usual with IPv6, you will also need to allow address resolution
(with IPv6 this is done "in band" using icmp6 packets which must be allowed