Enable to check capabilities per session with pola command

Enable to check capabilities per session with pola command.
relates to #41 

### Ex.
```bash
user@pce:~/pola/cmd/pola$ go run . session
sessionAddr(0): 10.100.0.1
  Capabilities: Stateful, Update, Segment-Routing, Instantiation
sessionAddr(1): 10.100.0.2
  Capabilities: Stateful, Update, Segment-Routing, Instantiation
```