When calling MdnsResponse.setInet4AddressRecord with null, the record
was removed from the records list, but not from the inet4AddressRecord /
inet6AddressRecord fields.
Fix that, and update the MdnsResponseDecoder test that missed the bug
because it modified the same incomplete MdnsResponse multiple times
(so isComplete keeps returning false), instead of using a copy of
a complete MdnsResponse.
This requires using a copy constructor, which will be useful for future
changes, so add it with a test.
Bug: 267570781
Test: atest
Change-Id: I199a8e4bc9a54a142c1fec1acee2ab6b1baa7efb
af4ea5826b