add show ip interfaces command

[batmancn]

- What I did

I add a command show ip interfaces to display L3 interface informations like IP.

- How I did it

Extends 'intfutil' and 'show/main.py' to add this fuction.

- How to verify it

# show ip interfaces
  Interface               IP    Oper    Admin                                       Description
-----------  ---------------  ------  -------  ------------------------------------------------
  Ethernet8   192.168.2.1/24    down       up                                               N/A
 Ethernet12   192.168.3.1/24    down       up                                               N/A
 Ethernet16   192.168.4.1/24    down       up                                               N/A
 Ethernet20   192.168.5.1/24    down       up                                               N/A
 Ethernet24   10.132.13.2/24    down       up                                               N/A
 Ethernet48   10.130.12.2/24    down       up                                               N/A
 Ethernet80  10.131.131.1/24    down       up                                               N/A
 Ethernet84  10.131.132.1/24    down       up                                               N/A
 Ethernet88  10.131.133.1/24    down       up                                               N/A
 Ethernet92  10.131.134.1/24    down       up                                               N/A
 Ethernet96  10.131.135.1/24    down       up                                               N/A
Ethernet100  10.131.136.1/24    down       up                                               N/A
Ethernet104  10.131.137.1/24    down       up                                               N/A
Ethernet108  10.131.138.1/24    down       up                                               N/A
Ethernet192   10.131.32.1/24    down       up  ...
Ethernet196   10.131.33.1/24    down       up  ...
Ethernet200   10.131.34.1/24    down       up  ...
Ethernet204   10.131.35.1/24    down       up  ...
Ethernet208   10.131.36.1/24    down       up  ...
Ethernet212       fc00:1::32    down       up  ...
    docker0   240.127.1.1/24     N/A      N/A                                               N/A
       eth0  172.18.8.213/24     N/A      N/A                                               N/A
         lo       10.131.3.1     N/A      N/A                                               N/A

[jleveque]

The command show ip interfaces already exists (it is the next command in this file, just below the get_if_admin_state() and get_if_oper_state() helper functions--line 898 in your modified file).

You're welcome to extend the existing command, but this PR is literally creating a second implementation of show ip interfaces.

[jleveque]

@batmancn: Have you seen my comment above? I suggest you close this PR and open a new one if you would like to extend the functionality of the existing show ip interfaces command.