lldpcli: reformat a bit bash completion to be more readable
lldpcli: change how privileged commands are declared

Even when not privileged, we declare privileged commands but tag them
accordingly. We need to be careful when executing the commands to check
the new bit.

This is a preliminary change to allow a completion command to complete
privileged commands even when not privileged.
lldpcli: provide a hidden complete command for shell completion
lldpcli: make complete command work on privleged commands as well

This avoids the use of sudo.