teamdctl: add command for easy port presention checking

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
initscripts: do not try to re-add port if it is already there

The thing is that first, the port is downed and after that the teamdctl
util is used to add it. When the port is already there, the only effect
is that the port goes down. Fix this by checking if port is already in team.

Signed-off-by: Jiri Pirko <jiri@resnulli.us>