peer: Improve net address service adverts.
peer: Improve net address service adverts.

This modifies the peer code which deals with advertising service flags
via the net address fields of the version message as follows:

- For outgoing connections:
  - Set the local netaddress services to what the local peer supports
  - Set the remote netaddress services to 0 to indicate no services as
    they are still unknown
- For incoming connections:
  - Set the local netaddress services to what the local peer supports
  - Set the remote netaddress services to the what was advertised by the
    remote peer in its version message

decred/dcrd,jrick/dcrd,jrick/dcrd,decred/dcrd