Fixes to IPv6 address handling

I've made some fixes to IPv6 address handling:

make address policy assume_action work for []-quoted IPv6 addresses
- unquoted addresses are ambiguous, because of the port separator ":", and "accept" starting with 4 hex digits
limit IPv6 mask bits to 128
warn when comparing against an AF_UNSPEC address in a policy
no code wants this to happen, and it produces unexpected results

Branch coming soon.

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