tc: add 'kind' property to 'csum' action

tc: add 'kind' property to 'csum' action

unlike other TC actions already supporting JSON printout, 'csum' does not
print the value of TCA_KIND in the 'kind' property: remove 'csum' word
from 'csum' property, and add a separate 'kind' property containing the
action name. The human-readable printout is preserved.

Tested with:
 # ./tdc.py -c csum

Cc: Andrea Claudi <aclaudi@redhat.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>