inbound: refactor newtypes for policy addresses

[hawkw]

Depends on #2186.

Currently, the linkerd-app-inbound crate's GetPolicy trait performs lookups for OrigDstAddrs. This is not strictly correct: the OrigDstAddr newtype should specifically represent an address that was returned by a getsockopt(..., SO_ORIGINAL_DST, ...) call, and in the case of the inbound direct stack, the "original dst address" passed to GetPolicy may actually be synthesized from a port override in the TransportHeader. Therefore, it would be nicer if we had a LookupAddr type specifically representing an address used as an argument for policy lookups, analogous to the profiles::LookupAddr newtype used on the outbound side. See this comment for details.

Therefore, this branch makes the following changes:

• Policy types (e.g. ServerPolicy, AllowPermit, etc) which store addresses represent those addresses as ServerAddr rather than OrigDstAddr, and perform address matching on ServerAddrs.
• The inbound::policy module now defines a LookupAddr newtype, which is passed as an argument to GetPolicy.
• The inbound accept and direct stacks provide ExtractParam impls to the policy::Discover layer indicating how LookupAddrs are produced from targets in that stack. This makes the different behaviors between the normal accept stack and the direct stack more explicit at the callsite.