ConnectionAdapterImpl fields should be private

This reduces visibility of protected fields to private, allowing us to
reason about their interactions.

Change-Id: Ie3954ad548c4fe20f98bda13cedf657513bd7d11
Signed-off-by: Robert Varga <rovarga@cisco.com>
Signed-off-by: Michal Polkorab <michal.polkorab@pantheon.sk>