[dropconfig] Clean-up error output for devices that do not support drop counters

[daall]

Signed-off-by: Danny Allen [email protected]

- What I did
I fixed the if-check for devices that do not publish any drop counter capabilities to state DB.

- How I did it
I added a return inside the if-check so that the function will stop if no capabilities are found.

- How to verify it
I ran the show dropcounters capabilities command immediately after boot to ensure that the CAPABILITIES table would be empty, triggering the if-check.

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

admin@sonic:~$ show dropcounters capabilities
Traceback (most recent call last):
  File "/usr/bin/dropconfig", line 414, in <module>
    main()
  File "/usr/bin/dropconfig", line 409, in main
    dconfig.print_device_capabilities()
  File "/usr/bin/dropconfig", line 97, in print_device_capabilities
Current device does not support drop counters
    for counter, capabilities in device_caps.iteritems():
AttributeError: 'NoneType' object has no attribute 'iteritems'

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

admin@sonic:~$ show dropcounters capabilities
Current device does not support drop counters

[daall]

retest this please