Fix show ip interfaces

[msosyak]

I faced the issue when call show ip interfaces on the latest SONiC image(03f82a0):

admin@sonic:~$ show ip interfaces 
sTraceback (most recent call last):
  File "/usr/local/bin/show", line 10, in <module>
    sys.exit(cli())
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/show/main.py", line 727, in interfaces
    netmask = netaddr.IPAddress(ipaddr['netmask']).netmask_bits()
NameError: global name 'netaddr' is not defined

In this PR netaddr was removed, but we need it to convert subnet mask to cidr here
- What I did
Fix NameError: global name 'netaddr' is not defined
- How I did it
import netaddr module
- How to verify it

• build SONiC with this changes or manually apply them in the running SONiC image
• run show ip interfaces
  - Previous command output (if the output of a command-line utility has changed)

admin@sonic:~$ show ip interfaces 
sTraceback (most recent call last):
  File "/usr/local/bin/show", line 10, in <module>
    sys.exit(cli())
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python2.7/dist-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/show/main.py", line 727, in interfaces
    netmask = netaddr.IPAddress(ipaddr['netmask']).netmask_bits()
NameError: global name 'netaddr' is not defined

- New command output (if the output of a command-line utility has changed)

admin@sonic:~$ show ip interfaces 
Interface    Master    IPv4 address/mask    Admin/Oper    BGP Neighbor    Neighbor IP
-----------  --------  -------------------  ------------  --------------  -------------
Ethernet0              10.0.0.1/24          up/up         N/A             N/A
Ethernet4              20.0.0.1/24          up/up         N/A             N/A
Ethernet8              10.0.0.4/31          up/up         ARISTA03T2      10.0.0.5
 * * *

[msosyak]

@arlakshm @jleveque Please review

[prsunny]

Thanks for fixing this.

[prsunny]

retest this please

[jleveque]

Closing as a duplicate of #1126, in which the new import is added in alphabetical order, whereas in this PR it is not.