Shorten the output of NetworkAgentInfo#toString().

Currently, printing a NetworkAgentInfo results in a very long
string. Make it a bit shorter by:

- Not printing a number of fields in NetworkInfo that are no
  longer used.
- Instead of printing flags regardless of whether they are true
  false, only print ones that are true. For example, this changes
    everCaptivePortalDetected{true} lastCaptivePortalDetected{false} captivePortalValidationPending{false}
  to:
    everCaptivePortalDetected
- Only printing clat information if clatd is started.

Also, put the long and variable-length fields lp and nc at the
end of the output.

Test: manual
Change-Id: I3312286be307ef1762890cbc6b717f12ce5b2b92