The pppoatm does not check if used vcc is in connected state,
causing an Oops in pppoatm_send() when vcc->send() is called
on not fully connected socket.
Now pppoatm can be assigned only on connected sockets; otherwise
-EINVAL error is returned.
Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net> Cc: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil> Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>